Re: [PATCH] struct page shrinkage

Re: [PATCH] struct page shrinkage

[Bulent Abali]

>Rik van Riel wrote:
>>
>> +               clear_bit(PG_locked, &p->flags);
>
>Please don't do this.  Please use the macros.  If they're not
>there, please create them.
>
>Bypassing the abstractions in this manner confounds people
>who are implementing global locked-page accounting.
>

Andrew,
I have an application which needs to know the total number of locked and
dirtied pages at any given time.  In which application locked-page
accounting is done?   I don't see it in base 2.5.5.   Are there any patches
or such that you can give pointers to?
Bulent


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Re: [PATCH] struct page shrinkage

[Andrew Morton]

Bulent Abali wrote:
> 
> >Rik van Riel wrote:
> >>
> >> +               clear_bit(PG_locked, &p->flags);
> >
> >Please don't do this.  Please use the macros.  If they're not
> >there, please create them.
> >
> >Bypassing the abstractions in this manner confounds people
> >who are implementing global locked-page accounting.
> >
> 
> Andrew,
> I have an application which needs to know the total number of locked and
> dirtied pages at any given time.  In which application locked-page
> accounting is done?   I don't see it in base 2.5.5.   Are there any patches
> or such that you can give pointers to?

This is in the ebulliently growing delayed-allocate and
buffer_head-bypass patches at

	http://www.zip.com.au/~akpm/linux/patches/2.5/2.5.6-pre2/

The implementation you're looking for is in dalloc-10-core.patch:
mm.h and mm/page_alloc.c

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Re: [PATCH] struct page shrinkage

[Rik van Riel]

On Wed, 6 Mar 2002, Bulent Abali wrote:
> >Rik van Riel wrote:
> >>
> >> +               clear_bit(PG_locked, &p->flags);
> >
> >Please don't do this.  Please use the macros.  If they're not
> >there, please create them.
> >
> >Bypassing the abstractions in this manner confounds people
> >who are implementing global locked-page accounting.
>
> I have an application which needs to know the total number of locked and
> dirtied pages at any given time.  In which application locked-page
> accounting is done?   I don't see it in base 2.5.5.   Are there any patches
> or such that you can give pointers to?

You could modify lock_page to do statistics. This is
made easier if you are sure that every driver uses
lock_page / LockPage and UnlockPage

I'm happy Andrew made me clean up the drivers instead
of just fixing them ;)

regards,

Rik
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Re: [PATCH] struct page shrinkage

[Bulent Abali]

>> Andrew,
>> I have an application which needs to know the total number of locked and
>> dirtied pages at any given time.  In which application locked-page
>> accounting is done?   I don't see it in base 2.5.5.   Are there any
patches
>> or such that you can give pointers to?
>
>This is in the ebulliently growing delayed-allocate and
>buffer_head-bypass patches at
>
> http://www.zip.com.au/~akpm/linux/patches/2.5/2.5.6-pre2/
>
>The implementation you're looking for is in dalloc-10-core.patch:
>mm.h and mm/page_alloc.c

extern struct page_state {
             unsigned long nr_dirty;
             unsigned long nr_locked;
} ____cacheline_aligned page_states[NR_CPUS];

This is perfect.   Looks like, if a run summation over all the CPUs I will
get the total locked and dirty pages, provided mm.h macros are respected.
What is the outlook for inclusion of this patch in the main kernel?  Do you
plan to submit or have been included yet?
Bulent




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Re: [PATCH] struct page shrinkage

[Mike Fedyk]

On Wed, Mar 06, 2002 at 01:41:51PM -0500, Bulent Abali wrote:
> What is the outlook for inclusion of this patch in the main kernel?  Do you
> plan to submit or have been included yet?

I believe it is planned to be submitted to 2.5.

Andrew, why isn't this listed on the 2.5 status page?
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Re: [PATCH] struct page shrinkage

[Andrew Morton]

Mike Fedyk wrote:
> 
> On Wed, Mar 06, 2002 at 01:41:51PM -0500, Bulent Abali wrote:
> > What is the outlook for inclusion of this patch in the main kernel?  Do you
> > plan to submit or have been included yet?
> 
> I believe it is planned to be submitted to 2.5.

hmm.

> Andrew, why isn't this listed on the 2.5 status page?

Coz it's something I pulled out of my butt just a couple of
weeks back :)

We'll see how it pans out.  I must say that after two years
of fixing other guys' bugs, it's fun writing some of my own.

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Re: [PATCH] struct page shrinkage

[Andrew Morton]

Bulent Abali wrote:
> 
> extern struct page_state {
>              unsigned long nr_dirty;
>              unsigned long nr_locked;
> } ____cacheline_aligned page_states[NR_CPUS];
> 
> This is perfect.   Looks like, if a run summation over all the CPUs I will
> get the total locked and dirty pages, provided mm.h macros are respected.

That's correct.  And the mm.h macros *are* respected.  That patch
ensures that they are.

It goes as far as to rename PG_locked and PG_dirty to PG_locked_dontuse
and PG_dirty_dontuse.

I'll be adding page_cache_size to the above struct, at least.

The "run summation" function is already there, btw: get_page_state().

> What is the outlook for inclusion of this patch in the main kernel?  Do you
> plan to submit or have been included yet?

Well it's all a part of a work to aggressively improve the efficiency
of regular file I/O.  I don't know if the big grand plan will be successful
yet.  At this time, it's thumbs up - way up.

Nor do I know if this is a direction in which Linus wishes to take
his kernel.

But this change, the readahead changes, the pdflush pool and a few other
pieces I have planned are probably appropriate for the base kernel
irrespective of the end outcome.

We'll see...

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[PATCH] struct page shrinkage

[Rik van Riel]

Hi Marcelo,

here is the struct page shrinkage patch against 2.4.19-pre1,
it does the following stuff:

 o page->wait is removed, instead we use a hash table of wait queues
   per zone ... collisions are ok because of wake-all semantics
 o page->virtual is only used on highmem machines and sparc64,
   other machines calculate the address instead
 o page->zone is folded into page->flags

Please apply for 2.4.19-pre2.

thank you,

Rik
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# This is a BitKeeper generated patch for the following project:
# Project Name: The Linux 2.4 Kernel
# This patch format is intended for GNU patch command version 2.5 or higher.
# This patch includes the following deltas:
#	           ChangeSet	1.156.1.2 -> 1.158
#	include/asm-sparc64/pgtable.h	1.14    -> 1.15
#	include/linux/mmzone.h	1.6     -> 1.7
#	drivers/char/agp/agpgart_be.c	1.22    -> 1.23
#	include/asm-s390/pgtable.h	1.4     -> 1.5
#	         mm/vmscan.c	1.56    -> 1.57
#	drivers/char/drm/i810_dma.c	1.5     -> 1.6
#	include/asm-i386/pgtable.h	1.4     -> 1.5
#	include/asm-s390x/pgtable.h	1.4     -> 1.5
#	include/asm-sparc/pgtable.h	1.4     -> 1.5
#	include/asm-sh/pgtable.h	1.6     -> 1.7
#	include/asm-arm/pgtable.h	1.5     -> 1.6
#	         fs/buffer.c	1.54    -> 1.55
#	        mm/filemap.c	1.53    -> 1.54
#	  include/linux/mm.h	1.34    -> 1.35
#	     mm/page_alloc.c	1.40    -> 1.41
#	include/asm-mips/pgtable.h	1.3     -> 1.4
#	drivers/char/drm-4.0/i810_dma.c	1.1     -> 1.2
#	include/linux/pagemap.h	1.16    -> 1.17
#	include/asm-alpha/pgtable.h	1.7     -> 1.8
#	         mm/Makefile	1.3.1.1 -> 1.5
#	include/asm-mips64/pgtable.h	1.3     -> 1.4
#	include/asm-sparc64/page.h	1.3     -> 1.4
#	include/asm-ia64/pgtable.h	1.6     -> 1.7
#	include/asm-cris/pgtable.h	1.5     -> 1.6
#	include/asm-parisc/pgtable.h	1.2     -> 1.3
#	include/asm-ppc/pgtable.h	1.7     -> 1.8
#
# The following is the BitKeeper ChangeSet Log
# --------------------------------------------
# 02/02/25	riel@imladris.surriel.com	1.158
# merge the mm/Makefile changes by hand
# --------------------------------------------
#
diff -Nru a/drivers/char/agp/agpgart_be.c b/drivers/char/agp/agpgart_be.c
--- a/drivers/char/agp/agpgart_be.c	Mon Feb 25 22:45:46 2002
+++ b/drivers/char/agp/agpgart_be.c	Mon Feb 25 22:45:46 2002
@@ -830,7 +830,7 @@
 	page = virt_to_page(pt);
 	atomic_dec(&page->count);
 	clear_bit(PG_locked, &page->flags);
-	wake_up(&page->wait);
+	wake_up_page(page);
 	free_page((unsigned long) pt);
 	atomic_dec(&agp_bridge.current_memory_agp);
 }
@@ -2835,7 +2835,7 @@
 	page = virt_to_page(pt);
 	atomic_dec(&page->count);
 	clear_bit(PG_locked, &page->flags);
-	wake_up(&page->wait);
+	wake_up_page(page);
 	free_page((unsigned long) pt);
 	atomic_dec(&agp_bridge.current_memory_agp);
 }
diff -Nru a/drivers/char/drm/i810_dma.c b/drivers/char/drm/i810_dma.c
--- a/drivers/char/drm/i810_dma.c	Mon Feb 25 22:45:46 2002
+++ b/drivers/char/drm/i810_dma.c	Mon Feb 25 22:45:46 2002
@@ -294,14 +294,13 @@

 static void i810_free_page(drm_device_t *dev, unsigned long page)
 {
-	if(page == 0UL)
-		return;
-
-	atomic_dec(&virt_to_page(page)->count);
-	clear_bit(PG_locked, &virt_to_page(page)->flags);
-	wake_up(&virt_to_page(page)->wait);
-	free_page(page);
-	return;
+	if (page) {
+		struct page *p = virt_to_page(page);
+		atomic_dec(p);
+		clear_bit(PG_locked, &p->flags);
+		wake_up_page(p);
+		free_page(page);
+	}
 }

 static int i810_dma_cleanup(drm_device_t *dev)
diff -Nru a/drivers/char/drm-4.0/i810_dma.c b/drivers/char/drm-4.0/i810_dma.c
--- a/drivers/char/drm-4.0/i810_dma.c	Mon Feb 25 22:45:46 2002
+++ b/drivers/char/drm-4.0/i810_dma.c	Mon Feb 25 22:45:46 2002
@@ -288,12 +288,13 @@

 static void i810_free_page(drm_device_t *dev, unsigned long page)
 {
+	struct page * p = virt_to_page(page);
 	if(page == 0UL)
 		return;

-	atomic_dec(&virt_to_page(page)->count);
-	clear_bit(PG_locked, &virt_to_page(page)->flags);
-	wake_up(&virt_to_page(page)->wait);
+	atomic_dec(p->count);
+	clear_bit(PG_locked, p->flags);
+	wake_up_page(p);
 	free_page(page);
 	return;
 }
diff -Nru a/fs/buffer.c b/fs/buffer.c
--- a/fs/buffer.c	Mon Feb 25 22:45:46 2002
+++ b/fs/buffer.c	Mon Feb 25 22:45:46 2002
@@ -2257,8 +2257,7 @@
  * of kiobuf structs (much like a user-space iovec list).
  *
  * The kiobuf must already be locked for IO.  IO is submitted
- * asynchronously: you need to check page->locked, page->uptodate, and
- * maybe wait on page->wait.
+ * asynchronously: you need to check page->locked and page->uptodate.
  *
  * It is up to the caller to make sure that there are enough blocks
  * passed in to completely map the iobufs to disk.
@@ -2391,8 +2390,8 @@
 /*
  * Start I/O on a page.
  * This function expects the page to be locked and may return
- * before I/O is complete. You then have to check page->locked,
- * page->uptodate, and maybe wait on page->wait.
+ * before I/O is complete. You then have to check page->locked
+ * and page->uptodate.
  *
  * brw_page() is SMP-safe, although it's being called with the
  * kernel lock held - but the code is ready.
diff -Nru a/include/asm-alpha/pgtable.h b/include/asm-alpha/pgtable.h
--- a/include/asm-alpha/pgtable.h	Mon Feb 25 22:45:46 2002
+++ b/include/asm-alpha/pgtable.h	Mon Feb 25 22:45:46 2002
@@ -268,8 +268,6 @@
 extern inline int pgd_present(pgd_t pgd)	{ return pgd_val(pgd) & _PAGE_VALID; }
 extern inline void pgd_clear(pgd_t * pgdp)	{ pgd_val(*pgdp) = 0; }

-#define page_address(page)	((page)->virtual)
-
 /*
  * The following only work if pte_present() is true.
  * Undefined behaviour if not..
diff -Nru a/include/asm-arm/pgtable.h b/include/asm-arm/pgtable.h
--- a/include/asm-arm/pgtable.h	Mon Feb 25 22:45:46 2002
+++ b/include/asm-arm/pgtable.h	Mon Feb 25 22:45:46 2002
@@ -98,7 +98,6 @@
 /*
  * Permanent address of a page. We never have highmem, so this is trivial.
  */
-#define page_address(page)	((page)->virtual)
 #define pages_to_mb(x)		((x) >> (20 - PAGE_SHIFT))

 /*
diff -Nru a/include/asm-cris/pgtable.h b/include/asm-cris/pgtable.h
--- a/include/asm-cris/pgtable.h	Mon Feb 25 22:45:46 2002
+++ b/include/asm-cris/pgtable.h	Mon Feb 25 22:45:46 2002
@@ -438,7 +438,6 @@

 /* permanent address of a page */

-#define page_address(page)      ((page)->virtual)
 #define __page_address(page)    (PAGE_OFFSET + (((page) - mem_map) << PAGE_SHIFT))
 #define pte_page(pte)           (mem_map+pte_pagenr(pte))

diff -Nru a/include/asm-i386/pgtable.h b/include/asm-i386/pgtable.h
--- a/include/asm-i386/pgtable.h	Mon Feb 25 22:45:46 2002
+++ b/include/asm-i386/pgtable.h	Mon Feb 25 22:45:46 2002
@@ -263,11 +263,7 @@
 #define pmd_clear(xp)	do { set_pmd(xp, __pmd(0)); } while (0)
 #define	pmd_bad(x)	((pmd_val(x) & (~PAGE_MASK & ~_PAGE_USER)) != _KERNPG_TABLE)

-/*
- * Permanent address of a page. Obviously must never be
- * called on a highmem page.
- */
-#define page_address(page) ((page)->virtual)
+
 #define pages_to_mb(x) ((x) >> (20-PAGE_SHIFT))

 /*
diff -Nru a/include/asm-ia64/pgtable.h b/include/asm-ia64/pgtable.h
--- a/include/asm-ia64/pgtable.h	Mon Feb 25 22:45:46 2002
+++ b/include/asm-ia64/pgtable.h	Mon Feb 25 22:45:46 2002
@@ -165,11 +165,6 @@
  * addresses:
  */

-/*
- * Given a pointer to an mem_map[] entry, return the kernel virtual
- * address corresponding to that page.
- */
-#define page_address(page)	((page)->virtual)

 /* Quick test to see if ADDR is a (potentially) valid physical address. */
 static inline long
diff -Nru a/include/asm-mips/pgtable.h b/include/asm-mips/pgtable.h
--- a/include/asm-mips/pgtable.h	Mon Feb 25 22:45:46 2002
+++ b/include/asm-mips/pgtable.h	Mon Feb 25 22:45:46 2002
@@ -329,11 +329,6 @@
 extern inline int pgd_present(pgd_t pgd)	{ return 1; }
 extern inline void pgd_clear(pgd_t *pgdp)	{ }

-/*
- * Permanent address of a page.  On MIPS we never have highmem, so this
- * is simple.
- */
-#define page_address(page)	((page)->virtual)
 #ifdef CONFIG_CPU_VR41XX
 #define pte_page(x)             (mem_map+(unsigned long)((pte_val(x) >> (PAGE_SHIFT + 2))))
 #else
diff -Nru a/include/asm-mips64/pgtable.h b/include/asm-mips64/pgtable.h
--- a/include/asm-mips64/pgtable.h	Mon Feb 25 22:45:46 2002
+++ b/include/asm-mips64/pgtable.h	Mon Feb 25 22:45:46 2002
@@ -366,11 +366,6 @@
 	pgd_val(*pgdp) = ((unsigned long) invalid_pmd_table);
 }

-/*
- * Permanent address of a page.  On MIPS64 we never have highmem, so this
- * is simple.
- */
-#define page_address(page)	((page)->virtual)
 #ifndef CONFIG_DISCONTIGMEM
 #define pte_page(x)		(mem_map+(unsigned long)((pte_val(x) >> PAGE_SHIFT)))
 #else
diff -Nru a/include/asm-parisc/pgtable.h b/include/asm-parisc/pgtable.h
--- a/include/asm-parisc/pgtable.h	Mon Feb 25 22:45:46 2002
+++ b/include/asm-parisc/pgtable.h	Mon Feb 25 22:45:46 2002
@@ -275,7 +275,6 @@
  * Permanent address of a page. Obviously must never be
  * called on a highmem page.
  */
-#define page_address(page) ({ if (!(page)->virtual) BUG(); (page)->virtual; })
 #define __page_address(page) ({ if (PageHighMem(page)) BUG(); PAGE_OFFSET + (((page) - mem_map) << PAGE_SHIFT); })
 #define pages_to_mb(x) ((x) >> (20-PAGE_SHIFT))
 #define pte_page(x) (mem_map+pte_pagenr(x))
diff -Nru a/include/asm-ppc/pgtable.h b/include/asm-ppc/pgtable.h
--- a/include/asm-ppc/pgtable.h	Mon Feb 25 22:45:46 2002
+++ b/include/asm-ppc/pgtable.h	Mon Feb 25 22:45:46 2002
@@ -341,10 +341,6 @@
 #define	pmd_present(pmd)	((pmd_val(pmd) & PAGE_MASK) != 0)
 #define	pmd_clear(pmdp)		do { pmd_val(*(pmdp)) = 0; } while (0)

-/*
- * Permanent address of a page.
- */
-#define page_address(page)	((page)->virtual)
 #define pte_page(x)		(mem_map+(unsigned long)((pte_val(x) >> PAGE_SHIFT)))

 #ifndef __ASSEMBLY__
diff -Nru a/include/asm-s390/pgtable.h b/include/asm-s390/pgtable.h
--- a/include/asm-s390/pgtable.h	Mon Feb 25 22:45:46 2002
+++ b/include/asm-s390/pgtable.h	Mon Feb 25 22:45:46 2002
@@ -238,10 +238,6 @@
 	*pteptr = pteval;
 }

-/*
- * Permanent address of a page.
- */
-#define page_address(page) ((page)->virtual)
 #define pages_to_mb(x) ((x) >> (20-PAGE_SHIFT))

 /*
diff -Nru a/include/asm-s390x/pgtable.h b/include/asm-s390x/pgtable.h
--- a/include/asm-s390x/pgtable.h	Mon Feb 25 22:45:46 2002
+++ b/include/asm-s390x/pgtable.h	Mon Feb 25 22:45:46 2002
@@ -233,10 +233,6 @@
 	*pteptr = pteval;
 }

-/*
- * Permanent address of a page.
- */
-#define page_address(page) ((page)->virtual)
 #define pages_to_mb(x) ((x) >> (20-PAGE_SHIFT))

 /*
diff -Nru a/include/asm-sh/pgtable.h b/include/asm-sh/pgtable.h
--- a/include/asm-sh/pgtable.h	Mon Feb 25 22:45:46 2002
+++ b/include/asm-sh/pgtable.h	Mon Feb 25 22:45:46 2002
@@ -206,11 +206,6 @@
 #define pmd_clear(xp)	do { set_pmd(xp, __pmd(0)); } while (0)
 #define	pmd_bad(x)	((pmd_val(x) & (~PAGE_MASK & ~_PAGE_USER)) != _KERNPG_TABLE)

-/*
- * Permanent address of a page. Obviously must never be
- * called on a highmem page.
- */
-#define page_address(page)  ((page)->virtual) /* P1 address of the page */
 #define pages_to_mb(x)	((x) >> (20-PAGE_SHIFT))
 #define pte_page(x) 	phys_to_page(pte_val(x)&PTE_PHYS_MASK)

diff -Nru a/include/asm-sparc/pgtable.h b/include/asm-sparc/pgtable.h
--- a/include/asm-sparc/pgtable.h	Mon Feb 25 22:45:46 2002
+++ b/include/asm-sparc/pgtable.h	Mon Feb 25 22:45:46 2002
@@ -293,9 +293,6 @@
 #define page_pte_prot(page, prot)	mk_pte(page, prot)
 #define page_pte(page)			page_pte_prot(page, __pgprot(0))

-/* Permanent address of a page. */
-#define page_address(page)  ((page)->virtual)
-
 BTFIXUPDEF_CALL(struct page *, pte_page, pte_t)
 #define pte_page(pte) BTFIXUP_CALL(pte_page)(pte)

diff -Nru a/include/asm-sparc64/page.h b/include/asm-sparc64/page.h
--- a/include/asm-sparc64/page.h	Mon Feb 25 22:45:46 2002
+++ b/include/asm-sparc64/page.h	Mon Feb 25 22:45:46 2002
@@ -30,6 +30,9 @@

 #define PAGE_BUG(page)	BUG()

+/* Sparc64 is slow at multiplication, we prefer to use some extra space. */
+#define WANT_PAGE_VIRTUAL 1
+
 extern void _clear_page(void *page);
 #define clear_page(X)	_clear_page((void *)(X))
 extern void clear_user_page(void *page, unsigned long vaddr);
diff -Nru a/include/asm-sparc64/pgtable.h b/include/asm-sparc64/pgtable.h
--- a/include/asm-sparc64/pgtable.h	Mon Feb 25 22:45:46 2002
+++ b/include/asm-sparc64/pgtable.h	Mon Feb 25 22:45:46 2002
@@ -243,8 +243,7 @@
 #define pte_mkold(pte)		(__pte(((pte_val(pte)<<1UL)>>1UL) & ~_PAGE_ACCESSED))

 /* Permanent address of a page. */
-#define __page_address(page)	((page)->virtual)
-#define page_address(page)	({ __page_address(page); })
+#define __page_address(page)	page_address(page)

 #define pte_page(x) (mem_map+(((pte_val(x)&_PAGE_PADDR)-phys_base)>>PAGE_SHIFT))

diff -Nru a/include/linux/mm.h b/include/linux/mm.h
--- a/include/linux/mm.h	Mon Feb 25 22:45:46 2002
+++ b/include/linux/mm.h	Mon Feb 25 22:45:46 2002
@@ -159,12 +159,23 @@
 					   updated asynchronously */
 	struct list_head lru;		/* Pageout list, eg. active_list;
 					   protected by pagemap_lru_lock !! */
-	wait_queue_head_t wait;		/* Page locked?  Stand in line... */
 	struct page **pprev_hash;	/* Complement to *next_hash. */
 	struct buffer_head * buffers;	/* Buffer maps us to a disk block. */
+
+	/*
+	 * On machines where all RAM is mapped into kernel address space,
+	 * we can simply calculate the virtual address. On machines with
+	 * highmem some memory is mapped into kernel virtual memory
+	 * dynamically, so we need a place to store that address.
+	 * Note that this field could be 16 bits on x86 ... ;)
+	 *
+	 * Architectures with slow multiplication can define
+	 * WANT_PAGE_VIRTUAL in asm/page.h
+	 */
+#if defined(CONFIG_HIGHMEM) || defined(WANT_PAGE_VIRTUAL)
 	void *virtual;			/* Kernel virtual address (NULL if
 					   not kmapped, ie. highmem) */
-	struct zone_struct *zone;	/* Memory zone we are in. */
+#endif /* CONFIG_HIGMEM || WANT_PAGE_VIRTUAL */
 } mem_map_t;

 /*
@@ -185,6 +196,11 @@
 #define page_count(p)		atomic_read(&(p)->count)
 #define set_page_count(p,v) 	atomic_set(&(p)->count, v)

+static inline void init_page_count(struct page *page)
+{
+	page->count.counter = 0;
+}
+
 /*
  * Various page->flags bits:
  *
@@ -239,7 +255,7 @@
  * - private pages which have been modified may need to be swapped out
  *   to swap space and (later) to be read back into memory.
  * During disk I/O, PG_locked is used. This bit is set before I/O
- * and reset when I/O completes. page->wait is a wait queue of all
+ * and reset when I/O completes. page_waitqueue(page) is a wait queue of all
  * tasks waiting for the I/O on this page to complete.
  * PG_uptodate tells whether the page's contents is valid.
  * When a read completes, the page becomes uptodate, unless a disk I/O
@@ -301,6 +317,61 @@
 #define SetPageChecked(page)	set_bit(PG_checked, &(page)->flags)
 #define PageLaunder(page)	test_bit(PG_launder, &(page)->flags)
 #define SetPageLaunder(page)	set_bit(PG_launder, &(page)->flags)
+#define __SetPageReserved(page)	__set_bit(PG_reserved, &(page)->flags)
+
+/*
+ * The zone field is never updated after free_area_init_core()
+ * sets it, so none of the operations on it need to be atomic.
+ */
+#define NODE_SHIFT 4
+#define ZONE_SHIFT (BITS_PER_LONG - 8)
+
+struct zone_struct;
+extern struct zone_struct *zone_table[];
+
+static inline zone_t *page_zone(struct page *page)
+{
+	return zone_table[page->flags >> ZONE_SHIFT];
+}
+
+static inline void set_page_zone(struct page *page, unsigned long zone_num)
+{
+	page->flags &= ~(~0UL << ZONE_SHIFT);
+	page->flags |= zone_num << ZONE_SHIFT;
+}
+
+/*
+ * In order to avoid #ifdefs within C code itself, we define
+ * set_page_address to a noop for non-highmem machines, where
+ * the field isn't useful.
+ * The same is true for page_address() in arch-dependent code.
+ */
+#if defined(CONFIG_HIGHMEM) || defined(WANT_PAGE_VIRTUAL)
+
+#define set_page_address(page, address)			\
+	do {						\
+		(page)->virtual = (address);		\
+	} while(0)
+
+#else /* CONFIG_HIGHMEM || WANT_PAGE_VIRTUAL */
+#define set_page_address(page, address)  do { } while(0)
+#endif /* CONFIG_HIGHMEM || WANT_PAGE_VIRTUAL */
+
+/*
+ * Permanent address of a page. Obviously must never be
+ * called on a highmem page.
+ */
+#if defined(CONFIG_HIGHMEM) || defined(WANT_PAGE_VIRTUAL)
+
+#define page_address(page) ((page)->virtual)
+
+#else /* CONFIG_HIGHMEM || WANT_PAGE_VIRTUAL */
+
+#define page_address(page)						\
+	__va( (((page) - page_zone(page)->zone_mem_map) << PAGE_SHIFT)	\
+			+ page_zone(page)->zone_start_paddr)
+
+#endif /* CONFIG_HIGHMEM || WANT_PAGE_VIRTUAL */

 extern void FASTCALL(set_page_dirty(struct page *));

diff -Nru a/include/linux/mmzone.h b/include/linux/mmzone.h
--- a/include/linux/mmzone.h	Mon Feb 25 22:45:46 2002
+++ b/include/linux/mmzone.h	Mon Feb 25 22:45:46 2002
@@ -7,6 +7,7 @@
 #include <linux/config.h>
 #include <linux/spinlock.h>
 #include <linux/list.h>
+#include <linux/wait.h>

 /*
  * Free memory management - zoned buddy allocator.
@@ -48,6 +49,35 @@
 	free_area_t		free_area[MAX_ORDER];

 	/*
+	 * wait_table		-- the array holding the hash table
+	 * wait_table_size	-- the size of the hash table array
+	 * wait_table_shift	-- wait_table_size
+	 * 				== BITS_PER_LONG (1 << wait_table_bits)
+	 *
+	 * The purpose of all these is to keep track of the people
+	 * waiting for a page to become available and make them
+	 * runnable again when possible. The trouble is that this
+	 * consumes a lot of space, especially when so few things
+	 * wait on pages at a given time. So instead of using
+	 * per-page waitqueues, we use a waitqueue hash table.
+	 *
+	 * The bucket discipline is to sleep on the same queue when
+	 * colliding and wake all in that wait queue when removing.
+	 * When something wakes, it must check to be sure its page is
+	 * truly available, a la thundering herd. The cost of a
+	 * collision is great, but given the expected load of the
+	 * table, they should be so rare as to be outweighed by the
+	 * benefits from the saved space.
+	 *
+	 * __wait_on_page() and unlock_page() in mm/filemap.c, are the
+	 * primary users of these fields, and in mm/page_alloc.c
+	 * free_area_init_core() performs the initialization of them.
+	 */
+	wait_queue_head_t	* wait_table;
+	unsigned long		wait_table_size;
+	unsigned long		wait_table_shift;
+
+	/*
 	 * Discontig memory support fields.
 	 */
 	struct pglist_data	*zone_pgdat;
@@ -132,10 +162,14 @@

 #define NODE_DATA(nid)		(&contig_page_data)
 #define NODE_MEM_MAP(nid)	mem_map
+#define MAX_NR_NODES		1

 #else /* !CONFIG_DISCONTIGMEM */

 #include <asm/mmzone.h>
+
+/* page->zone is currently 8 bits ... */
+#define MAX_NR_NODES		(255 / MAX_NR_ZONES)

 #endif /* !CONFIG_DISCONTIGMEM */

diff -Nru a/include/linux/pagemap.h b/include/linux/pagemap.h
--- a/include/linux/pagemap.h	Mon Feb 25 22:45:46 2002
+++ b/include/linux/pagemap.h	Mon Feb 25 22:45:46 2002
@@ -97,6 +97,8 @@
 		___wait_on_page(page);
 }

+extern void wake_up_page(struct page *);
+
 extern struct page * grab_cache_page (struct address_space *, unsigned long);
 extern struct page * grab_cache_page_nowait (struct address_space *, unsigned long);

diff -Nru a/mm/Makefile b/mm/Makefile
--- a/mm/Makefile	Mon Feb 25 22:45:46 2002
+++ b/mm/Makefile	Mon Feb 25 22:45:46 2002
@@ -9,7 +9,7 @@

 O_TARGET := mm.o

-export-objs := shmem.o filemap.o memory.o
+export-objs := shmem.o filemap.o memory.o page_alloc.o

 obj-y	 := memory.o mmap.o filemap.o mprotect.o mlock.o mremap.o \
 	    vmalloc.o slab.o bootmem.o swap.o vmscan.o page_io.o \
diff -Nru a/mm/filemap.c b/mm/filemap.c
--- a/mm/filemap.c	Mon Feb 25 22:45:46 2002
+++ b/mm/filemap.c	Mon Feb 25 22:45:46 2002
@@ -745,6 +745,67 @@
 	return 0;
 }

+/*
+ * Knuth recommends primes in approximately golden ratio to the maximum
+ * integer representable by a machine word for multiplicative hashing.
+ * Chuck Lever verified the effectiveness of this technique:
+ * http://www.citi.umich.edu/techreports/reports/citi-tr-00-1.pdf
+ *
+ * These primes are chosen to be bit-sparse, that is operations on
+ * them can use shifts and additions instead of multiplications for
+ * machines where multiplications are slow.
+ */
+#if BITS_PER_LONG == 32
+/* 2^31 + 2^29 - 2^25 + 2^22 - 2^19 - 2^16 + 1 */
+#define GOLDEN_RATIO_PRIME 0x9e370001UL
+#elif BITS_PER_LONG == 64
+/*  2^63 + 2^61 - 2^57 + 2^54 - 2^51 - 2^18 + 1 */
+#define GOLDEN_RATIO_PRIME 0x9e37fffffffc0001UL
+#else
+#error Define GOLDEN_RATIO_PRIME for your wordsize.
+#endif
+
+/*
+ * In order to wait for pages to become available there must be
+ * waitqueues associated with pages. By using a hash table of
+ * waitqueues where the bucket discipline is to maintain all
+ * waiters on the same queue and wake all when any of the pages
+ * become available, and for the woken contexts to check to be
+ * sure the appropriate page became available, this saves space
+ * at a cost of "thundering herd" phenomena during rare hash
+ * collisions.
+ */
+static inline wait_queue_head_t *page_waitqueue(struct page *page)
+{
+	const zone_t *zone = page_zone(page);
+	wait_queue_head_t *wait = zone->wait_table;
+	unsigned long hash = (unsigned long)page;
+
+#if BITS_PER_LONG == 64
+	/*  Sigh, gcc can't optimise this alone like it does for 32 bits. */
+	unsigned long n = hash;
+	n <<= 18;
+	hash -= n;
+	n <<= 33;
+	hash -= n;
+	n <<= 3;
+	hash += n;
+	n <<= 3;
+	hash -= n;
+	n <<= 4;
+	hash += n;
+	n <<= 2;
+	hash += n;
+#else
+	/* On some cpus multiply is faster, on others gcc will do shifts */
+	hash *= GOLDEN_RATIO_PRIME;
+#endif
+
+	hash >>= zone->wait_table_shift;
+
+	return &wait[hash];
+}
+
 /*
  * Wait for a page to get unlocked.
  *
@@ -754,10 +815,11 @@
  */
 void ___wait_on_page(struct page *page)
 {
+	wait_queue_head_t *waitqueue = page_waitqueue(page);
 	struct task_struct *tsk = current;
 	DECLARE_WAITQUEUE(wait, tsk);

-	add_wait_queue(&page->wait, &wait);
+	add_wait_queue(waitqueue, &wait);
 	do {
 		set_task_state(tsk, TASK_UNINTERRUPTIBLE);
 		if (!PageLocked(page))
@@ -765,19 +827,23 @@
 		sync_page(page);
 		schedule();
 	} while (PageLocked(page));
-	tsk->state = TASK_RUNNING;
-	remove_wait_queue(&page->wait, &wait);
+	__set_task_state(tsk, TASK_RUNNING);
+	remove_wait_queue(waitqueue, &wait);
 }

+/*
+ * Unlock the page and wake up sleepers in ___wait_on_page.
+ */
 void unlock_page(struct page *page)
 {
+	wait_queue_head_t *waitqueue = page_waitqueue(page);
 	clear_bit(PG_launder, &(page)->flags);
 	smp_mb__before_clear_bit();
 	if (!test_and_clear_bit(PG_locked, &(page)->flags))
 		BUG();
 	smp_mb__after_clear_bit();
-	if (waitqueue_active(&(page)->wait))
-	wake_up(&(page)->wait);
+	if (waitqueue_active(waitqueue))
+		wake_up_all(waitqueue);
 }

 /*
@@ -786,10 +852,11 @@
  */
 static void __lock_page(struct page *page)
 {
+	wait_queue_head_t *waitqueue = page_waitqueue(page);
 	struct task_struct *tsk = current;
 	DECLARE_WAITQUEUE(wait, tsk);

-	add_wait_queue_exclusive(&page->wait, &wait);
+	add_wait_queue_exclusive(waitqueue, &wait);
 	for (;;) {
 		set_task_state(tsk, TASK_UNINTERRUPTIBLE);
 		if (PageLocked(page)) {
@@ -799,10 +866,15 @@
 		if (!TryLockPage(page))
 			break;
 	}
-	tsk->state = TASK_RUNNING;
-	remove_wait_queue(&page->wait, &wait);
+	__set_task_state(tsk, TASK_RUNNING);
+	remove_wait_queue(waitqueue, &wait);
+}
+
+void wake_up_page(struct page *page)
+{
+	wake_up(page_waitqueue(page));
 }
-
+EXPORT_SYMBOL(wake_up_page);

 /*
  * Get an exclusive lock on the page, optimistically
diff -Nru a/mm/page_alloc.c b/mm/page_alloc.c
--- a/mm/page_alloc.c	Mon Feb 25 22:45:46 2002
+++ b/mm/page_alloc.c	Mon Feb 25 22:45:46 2002
@@ -1,6 +1,9 @@
 /*
  *  linux/mm/page_alloc.c
  *
+ *  Manages the free list, the system allocates free pages here.
+ *  Note that kmalloc() lives in slab.c
+ *
  *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
  *  Swap reorganised 29.12.95, Stephen Tweedie
  *  Support of BIGMEM added by Gerhard Wichert, Siemens AG, July 1999
@@ -18,6 +21,7 @@
 #include <linux/bootmem.h>
 #include <linux/slab.h>
 #include <linux/compiler.h>
+#include <linux/module.h>

 int nr_swap_pages;
 int nr_active_pages;
@@ -26,6 +30,10 @@
 struct list_head active_list;
 pg_data_t *pgdat_list;

+/* Used to look up the address of the struct zone encoded in page->zone */
+zone_t *zone_table[MAX_NR_ZONES*MAX_NR_NODES];
+EXPORT_SYMBOL(zone_table);
+
 static char *zone_names[MAX_NR_ZONES] = { "DMA", "Normal", "HighMem" };
 static int zone_balance_ratio[MAX_NR_ZONES] __initdata = { 128, 128, 128, };
 static int zone_balance_min[MAX_NR_ZONES] __initdata = { 20 , 20, 20, };
@@ -54,12 +62,31 @@
 /*
  * Temporary debugging check.
  */
-#define BAD_RANGE(zone,x) (((zone) != (x)->zone) || (((x)-mem_map) < (zone)->zone_start_mapnr) || (((x)-mem_map) >= (zone)->zone_start_mapnr+(zone)->size))
+#define BAD_RANGE(zone, page)						\
+(									\
+	(((page) - mem_map) >= ((zone)->zone_start_mapnr+(zone)->size))	\
+	|| (((page) - mem_map) < (zone)->zone_start_mapnr)		\
+	|| ((zone) != page_zone(page))					\
+)

 /*
- * Buddy system. Hairy. You really aren't expected to understand this
+ * Freeing function for a buddy system allocator.
+ *
+ * The concept of a buddy system is to maintain direct-mapped table
+ * (containing bit values) for memory blocks of various "orders".
+ * The bottom level table contains the map for the smallest allocatable
+ * units of memory (here, pages), and each level above it describes
+ * pairs of units from the levels below, hence, "buddies".
+ * At a high level, all that happens here is marking the table entry
+ * at the bottom level available, and propagating the changes upward
+ * as necessary, plus some accounting needed to play nicely with other
+ * parts of the VM system.
+ *
+ * TODO: give references to descriptions of buddy system allocators,
+ * describe precisely the silly trick buddy allocators use to avoid
+ * storing an extra bit, utilizing entry point information.
  *
- * Hint: -mask = 1+~mask
+ * -- wli
  */

 static void FASTCALL(__free_pages_ok (struct page *page, unsigned int order));
@@ -96,7 +123,7 @@
 		goto local_freelist;
  back_local_freelist:

-	zone = page->zone;
+	zone = page_zone(page);

 	mask = (~0UL) << order;
 	base = zone->zone_mem_map;
@@ -123,6 +150,8 @@
 			break;
 		/*
 		 * Move the buddy up one level.
+		 * This code is taking advantage of the identity:
+		 * 	-mask = 1+~mask
 		 */
 		buddy1 = base + (page_idx ^ -mask);
 		buddy2 = base + page_idx;
@@ -261,7 +290,7 @@
 			entry = local_pages->next;
 			do {
 				tmp = list_entry(entry, struct page, list);
-				if (tmp->index == order && memclass(tmp->zone, classzone)) {
+				if (tmp->index == order && memclass(page_zone(tmp), classzone)) {
 					list_del(entry);
 					current->nr_local_pages--;
 					set_page_count(tmp, 1);
@@ -623,6 +652,48 @@
 	}
 }

+/*
+ * Helper functions to size the waitqueue hash table.
+ * Essentially these want to choose hash table sizes sufficiently
+ * large so that collisions trying to wait on pages are rare.
+ * But in fact, the number of active page waitqueues on typical
+ * systems is ridiculously low, less than 200. So this is even
+ * conservative, even though it seems large.
+ *
+ * The constant PAGES_PER_WAITQUEUE specifies the ratio of pages to
+ * waitqueues, i.e. the size of the waitq table given the number of pages.
+ */
+#define PAGES_PER_WAITQUEUE	256
+
+static inline unsigned long wait_table_size(unsigned long pages)
+{
+	unsigned long size = 1;
+
+	pages /= PAGES_PER_WAITQUEUE;
+
+	while (size < pages)
+		size <<= 1;
+
+	/*
+	 * Once we have dozens or even hundreds of threads sleeping
+	 * on IO we've got bigger problems than wait queue collision.
+	 * Limit the size of the wait table to a reasonable size.
+	 */
+	size = min(size, 4096UL);
+
+	return size;
+}
+
+/*
+ * This is an integer logarithm so that shifts can be used later
+ * to extract the more random high bits from the multiplicative
+ * hash function before the remainder is taken.
+ */
+static inline unsigned long wait_table_bits(unsigned long size)
+{
+	return ffz(~size);
+}
+
 #define LONG_ALIGN(x) (((x)+(sizeof(long))-1)&~((sizeof(long))-1))

 /*
@@ -635,7 +706,6 @@
 	unsigned long *zones_size, unsigned long zone_start_paddr,
 	unsigned long *zholes_size, struct page *lmem_map)
 {
-	struct page *p;
 	unsigned long i, j;
 	unsigned long map_size;
 	unsigned long totalpages, offset, realtotalpages;
@@ -678,24 +748,13 @@
 	pgdat->node_start_mapnr = (lmem_map - mem_map);
 	pgdat->nr_zones = 0;

-	/*
-	 * Initially all pages are reserved - free ones are freed
-	 * up by free_all_bootmem() once the early boot process is
-	 * done.
-	 */
-	for (p = lmem_map; p < lmem_map + totalpages; p++) {
-		set_page_count(p, 0);
-		SetPageReserved(p);
-		init_waitqueue_head(&p->wait);
-		memlist_init(&p->list);
-	}
-
 	offset = lmem_map - mem_map;
 	for (j = 0; j < MAX_NR_ZONES; j++) {
 		zone_t *zone = pgdat->node_zones + j;
 		unsigned long mask;
 		unsigned long size, realsize;

+		zone_table[nid * MAX_NR_ZONES + j] = zone;
 		realsize = size = zones_size[j];
 		if (zholes_size)
 			realsize -= zholes_size[j];
@@ -710,6 +769,20 @@
 		if (!size)
 			continue;

+		/*
+		 * The per-page waitqueue mechanism uses hashed waitqueues
+		 * per zone.
+		 */
+		zone->wait_table_size = wait_table_size(size);
+		zone->wait_table_shift =
+			BITS_PER_LONG - wait_table_bits(zone->wait_table_size);
+		zone->wait_table = (wait_queue_head_t *)
+			alloc_bootmem_node(pgdat, zone->wait_table_size
+						* sizeof(wait_queue_head_t));
+
+		for(i = 0; i < zone->wait_table_size; ++i)
+			init_waitqueue_head(zone->wait_table + i);
+
 		pgdat->nr_zones = j+1;

 		mask = (realsize / zone_balance_ratio[j]);
@@ -728,11 +801,19 @@
 		if ((zone_start_paddr >> PAGE_SHIFT) & (zone_required_alignment-1))
 			printk("BUG: wrong zone alignment, it will crash\n");

+		/*
+		 * Initially all pages are reserved - free ones are freed
+		 * up by free_all_bootmem() once the early boot process is
+		 * done. Non-atomic initialization, single-pass.
+		 */
 		for (i = 0; i < size; i++) {
 			struct page *page = mem_map + offset + i;
-			page->zone = zone;
+			set_page_zone(page, nid * MAX_NR_ZONES + j);
+			init_page_count(page);
+			__SetPageReserved(page);
+			memlist_init(&page->list);
 			if (j != ZONE_HIGHMEM)
-				page->virtual = __va(zone_start_paddr);
+				set_page_address(page, __va(zone_start_paddr));
 			zone_start_paddr += PAGE_SIZE;
 		}

diff -Nru a/mm/vmscan.c b/mm/vmscan.c
--- a/mm/vmscan.c	Mon Feb 25 22:45:46 2002
+++ b/mm/vmscan.c	Mon Feb 25 22:45:46 2002
@@ -58,7 +58,7 @@
 		return 0;

 	/* Don't bother replenishing zones not under pressure.. */
-	if (!memclass(page->zone, classzone))
+	if (!memclass(page_zone(page), classzone))
 		return 0;

 	if (TryLockPage(page))
@@ -369,7 +369,7 @@
 		if (unlikely(!page_count(page)))
 			continue;

-		if (!memclass(page->zone, classzone))
+		if (!memclass(page_zone(page), classzone))
 			continue;

 		/* Racy check to avoid trylocking when not worthwhile */

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Re: [PATCH] struct page shrinkage

[David S. Miller]

   Please apply for 2.4.19-pre2.

Please fix the atomic_t assumptions in init_page_count() first.
You should be using atomic_set(...).

Franks a lot,
David S. Miller
davem@redhat.com
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Re: [PATCH] struct page shrinkage

[Rik van Riel]

On Mon, 25 Feb 2002, David S. Miller wrote:

>    From: Rik van Riel <riel@conectiva.com.br>
>    Date: Mon, 25 Feb 2002 22:47:00 -0300 (BRT)
>
>    Please apply for 2.4.19-pre2.
>
> Please fix the atomic_t assumptions in init_page_count() first.
> You should be using atomic_set(...).

Why ?   You'll see init_page_count() is _only_ used from
free_area_init_core(), when nothing else is using the VM
yet.

This exact same code has been in -rmap for a few months
and went into 2.5 just over a week ago.  It doesn't seem
to give any problems ...

regards,

Rik
-- 
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    -- Microsoft's "Competing with Linux" document

http://www.surriel.com/		http://distro.conectiva.com/

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Re: [PATCH] struct page shrinkage

[David S. Miller]

   On Mon, 25 Feb 2002, David S. Miller wrote:
   
   > Please fix the atomic_t assumptions in init_page_count() first.
   > You should be using atomic_set(...).
   
   Why ?   You'll see init_page_count() is _only_ used from
   free_area_init_core(), when nothing else is using the VM
   yet.
   
Rik, not every architecture has a "counter" member of
atomic_t, that is the problem.  This is a hard bug, please
fix it.  It is an opaque type, accessing its' implementation
directly is therefore illegal in the strongest way possible.

   This exact same code has been in -rmap for a few months
   and went into 2.5 just over a week ago.  It doesn't seem
   to give any problems ...

Because I haven't pushed my sparc64 changesets yet, I'm doing
that tonight.

Franks a lot,
David S. Miller
davem@redhat.com
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Re: [PATCH] struct page shrinkage

[Rik van Riel]

On Mon, 25 Feb 2002, David S. Miller wrote:
>  From: Rik van Riel <riel@conectiva.com.br>
>    On Mon, 25 Feb 2002, David S. Miller wrote:
>
>    > Please fix the atomic_t assumptions in init_page_count() first.
>    > You should be using atomic_set(...).
>
>    Why ?   You'll see init_page_count() is _only_ used from
>    free_area_init_core(), when nothing else is using the VM
>    yet.
>
> Rik, not every architecture has a "counter" member of
> atomic_t, that is the problem.  This is a hard bug, please
> fix it.  It is an opaque type, accessing its' implementation
> directly is therefore illegal in the strongest way possible.

OK, agreed.   I'm making a new patch right now.

regards,

Rik
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Re: [PATCH] struct page shrinkage

[William Lee Irwin III]

On Mon, Feb 25, 2002 at 06:01:22PM -0800, David S. Miller wrote:
> Rik, not every architecture has a "counter" member of
> atomic_t, that is the problem.  This is a hard bug, please
> fix it.  It is an opaque type, accessing its' implementation
> directly is therefore illegal in the strongest way possible.

> From: Rik van Riel <riel@conectiva.com.br>
> This exact same code has been in -rmap for a few months
> and went into 2.5 just over a week ago.  It doesn't seem
> to give any problems ...

On Mon, Feb 25, 2002 at 06:01:22PM -0800, David S. Miller wrote:
> Because I haven't pushed my sparc64 changesets yet, I'm doing
> that tonight.

I think I'm to blame for init_page_count(). My bad.

A small bit of analysis seemed to reveal that atomicity wasn't needed
in free_area_init_core(). Apparently the solution I suggested here was
non-portable. Perhaps a better way will crop up later.

Cheers,
Bill
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Re: [PATCH] struct page shrinkage

[Andrew Morton]

Rik van Riel wrote:
> 
> +               clear_bit(PG_locked, &p->flags);

Please don't do this.  Please use the macros.  If they're not
there, please create them.

Bypassing the abstractions in this manner confounds people
who are implementing global locked-page accounting.

In fact, I think I'll go rename all the page flags...

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Re: [PATCH] struct page shrinkage

[William Lee Irwin III]

Rik van Riel wrote:
>> 
>> +               clear_bit(PG_locked, &p->flags);

On Mon, Feb 25, 2002 at 06:16:49PM -0800, Andrew Morton wrote:
> Please don't do this.  Please use the macros.  If they're not
> there, please create them.
> 
> Bypassing the abstractions in this manner confounds people
> who are implementing global locked-page accounting.
> 
> In fact, I think I'll go rename all the page flags...

This is lingering context from the driver... it's ugly, I didn't
go after cleaning that up when I had to touch this function because
of the usual minimal-impact / only do one thing principle.

Perhaps others were similarly (un)motivated.


Cheers,
Bill
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