[PATCH] memcg: fix to leave pages on wrong LRU with FUSE.

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* [PATCH] memcg: fix to leave pages on wrong LRU with FUSE.
@ 2011-03-07  6:00 KAMEZAWA Hiroyuki
  2011-03-08  0:59 ` Daisuke Nishimura
  0 siblings, 1 reply; 5+ messages in thread
From: KAMEZAWA Hiroyuki @ 2011-03-07  6:00 UTC (permalink / raw)
  To: linux-mm; +Cc: nishimura, balbir, akpm, miklos

At this point, I'm not sure this is a fix for 
   https://bugzilla.kernel.org/show_bug.cgi?id=30432.

The behavior seems very similar to SwapCache case and this is a possible
bug and this patch can be a fix. Nishimura-san, how do you think ?

But I'm not sure how to test this....please review.

=
fs/fuse/dev.c::fuse_try_move_page() does

   (1) remove a page from page cache by ->steal()
   (2) re-add the page to page cache 
   (3) link the page to LRU if it was _not_ on LRU at (1)


This implies the page can be _on_ LRU when add_to_page_cache_locked() is called.
So, the page is added to a memory cgroup while it's on LRU.

This is the same behavior as SwapCache, 'newly charged pages may be on LRU'
and needs special care as
 - remove page from old memcg's LRU before overwrite pc->mem_cgroup.
 - add page to new memcg's LRU after overwrite pc->mem_cgroup.

So, reusing SwapCache code with renaming for fix.

Note: a page on pagevec(LRU).

If a page is not PageLRU(page) but on pagevec(LRU), it may be added to LRU
while we overwrite page->mapping. But in that case, PCG_USED bit of
the page_cgroup is not set and the page_cgroup will not be added to
wrong memcg's LRU. So, this patch's logic will work fine.
(It has been tested with SwapCache.)

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
 mm/memcontrol.c |   42 +++++++++++++++++++++++-------------------
 1 file changed, 23 insertions(+), 19 deletions(-)

Index: mmotm-0303/mm/memcontrol.c
===================================================================
--- mmotm-0303.orig/mm/memcontrol.c
+++ mmotm-0303/mm/memcontrol.c
@@ -926,13 +926,12 @@ void mem_cgroup_add_lru_list(struct page
 }
 
 /*
- * At handling SwapCache, pc->mem_cgroup may be changed while it's linked to
- * lru because the page may.be reused after it's fully uncharged (because of
- * SwapCache behavior).To handle that, unlink page_cgroup from LRU when charge
- * it again. This function is only used to charge SwapCache. It's done under
- * lock_page and expected that zone->lru_lock is never held.
+ * At handling SwapCache and other FUSE stuff, pc->mem_cgroup may be changed
+ * while it's linked to lru because the page may be reused after it's fully
+ * uncharged. To handle that, unlink page_cgroup from LRU when charge it again.
+ * It's done under lock_page and expected that zone->lru_lock isnever held.
  */
-static void mem_cgroup_lru_del_before_commit_swapcache(struct page *page)
+static void mem_cgroup_lru_del_before_commit(struct page *page)
 {
 	unsigned long flags;
 	struct zone *zone = page_zone(page);
@@ -948,7 +947,7 @@ static void mem_cgroup_lru_del_before_co
 	spin_unlock_irqrestore(&zone->lru_lock, flags);
 }
 
-static void mem_cgroup_lru_add_after_commit_swapcache(struct page *page)
+static void mem_cgroup_lru_add_after_commit(struct page *page)
 {
 	unsigned long flags;
 	struct zone *zone = page_zone(page);
@@ -2428,7 +2427,7 @@ int mem_cgroup_newpage_charge(struct pag
 }
 
 static void
-__mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr,
+__mem_cgroup_commit_charge_lrucare(struct page *page, struct mem_cgroup *ptr,
 					enum charge_type ctype);
 
 int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
@@ -2468,17 +2467,22 @@ int mem_cgroup_cache_charge(struct page 
 	if (unlikely(!mm))
 		mm = &init_mm;
 
-	if (page_is_file_cache(page))
-		return mem_cgroup_charge_common(page, mm, gfp_mask,
+	if (page_is_file_cache(page) && !PageLRU(page)) {
+		ret = mem_cgroup_charge_common(page, mm, gfp_mask,
 				MEM_CGROUP_CHARGE_TYPE_CACHE);
-
-	/* shmem */
-	if (PageSwapCache(page)) {
+	} else if (page_is_file_cache(page)) {
+		struct mem_cgroup *mem;
+		/* Page on LRU should be moved to the _new_ LRU */
+		ret = __mem_cgroup_try_charge(mm, gfp_mask, 1, &mem, true);
+		if (!ret)
+			__mem_cgroup_commit_charge_lrucare(page, mem,
+					MEM_CGROUP_CHARGE_TYPE_CACHE);
+	} else if (PageSwapCache(page)) {
 		struct mem_cgroup *mem;
-
 		ret = mem_cgroup_try_charge_swapin(mm, page, gfp_mask, &mem);
+
 		if (!ret)
-			__mem_cgroup_commit_charge_swapin(page, mem,
+			__mem_cgroup_commit_charge_lrucare(page, mem,
 					MEM_CGROUP_CHARGE_TYPE_SHMEM);
 	} else
 		ret = mem_cgroup_charge_common(page, mm, gfp_mask,
@@ -2529,7 +2533,7 @@ charge_cur_mm:
 }
 
 static void
-__mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr,
+__mem_cgroup_commit_charge_lrucare(struct page *page, struct mem_cgroup *ptr,
 					enum charge_type ctype)
 {
 	struct page_cgroup *pc;
@@ -2540,9 +2544,9 @@ __mem_cgroup_commit_charge_swapin(struct
 		return;
 	cgroup_exclude_rmdir(&ptr->css);
 	pc = lookup_page_cgroup(page);
-	mem_cgroup_lru_del_before_commit_swapcache(page);
+	mem_cgroup_lru_del_before_commit(page);
 	__mem_cgroup_commit_charge(ptr, page, 1, pc, ctype);
-	mem_cgroup_lru_add_after_commit_swapcache(page);
+	mem_cgroup_lru_add_after_commit(page);
 	/*
 	 * Now swap is on-memory. This means this page may be
 	 * counted both as mem and swap....double count.
@@ -2580,7 +2584,7 @@ __mem_cgroup_commit_charge_swapin(struct
 
 void mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr)
 {
-	__mem_cgroup_commit_charge_swapin(page, ptr,
+	__mem_cgroup_commit_charge_lrucare(page, ptr,
 					MEM_CGROUP_CHARGE_TYPE_MAPPED);
 }
 

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^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [PATCH] memcg: fix to leave pages on wrong LRU with FUSE.
  2011-03-07  6:00 [PATCH] memcg: fix to leave pages on wrong LRU with FUSE KAMEZAWA Hiroyuki
@ 2011-03-08  0:59 ` Daisuke Nishimura
  2011-03-08  1:02   ` KAMEZAWA Hiroyuki
  0 siblings, 1 reply; 5+ messages in thread
From: Daisuke Nishimura @ 2011-03-08  0:59 UTC (permalink / raw)
  To: KAMEZAWA Hiroyuki; +Cc: linux-mm, balbir, akpm, miklos, Daisuke Nishimura

On Mon, 7 Mar 2011 15:00:49 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:

> At this point, I'm not sure this is a fix for 
>    https://bugzilla.kernel.org/show_bug.cgi?id=30432.
> 
> The behavior seems very similar to SwapCache case and this is a possible
> bug and this patch can be a fix. Nishimura-san, how do you think ?
> 
As long as I can read the source code, I also think this is a possible bug.

> But I'm not sure how to test this....please review.
> 
> =
> fs/fuse/dev.c::fuse_try_move_page() does
> 
>    (1) remove a page from page cache by ->steal()
>    (2) re-add the page to page cache 
>    (3) link the page to LRU if it was _not_ on LRU at (1)
> 
> 
> This implies the page can be _on_ LRU when add_to_page_cache_locked() is called.
> So, the page is added to a memory cgroup while it's on LRU.
> 
> This is the same behavior as SwapCache, 'newly charged pages may be on LRU'
> and needs special care as
>  - remove page from old memcg's LRU before overwrite pc->mem_cgroup.
>  - add page to new memcg's LRU after overwrite pc->mem_cgroup.
> 
> So, reusing SwapCache code with renaming for fix.
> 
> Note: a page on pagevec(LRU).
> 
> If a page is not PageLRU(page) but on pagevec(LRU), it may be added to LRU
> while we overwrite page->mapping. But in that case, PCG_USED bit of
> the page_cgroup is not set and the page_cgroup will not be added to
> wrong memcg's LRU. So, this patch's logic will work fine.
> (It has been tested with SwapCache.)
> 
As for SwapCache, mem_cgroup_lru_add_after_commit() will be allways called,
and it will link the page to LRU. But, if I read this patch correctly,
a page cache on pagevec may not be added to a *proper* memcg's LRU.

      lru_add_drain()           mem_cgroup_cache_charge()
  ----------------------------------------------------------
                                  if (!PageLRU())
    SetPageLRU()
    add_page_to_lru_list()
      mem_cgroup_add_lru_list()
      -> do nothing
                                    mem_cgroup_charge_common()
                                      mem_cgroup_commit_charge()
                                      -> set PCG_USED

Right ?

Thanks,
Daisuke Nishimura.

> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> ---
>  mm/memcontrol.c |   42 +++++++++++++++++++++++-------------------
>  1 file changed, 23 insertions(+), 19 deletions(-)
> 
> Index: mmotm-0303/mm/memcontrol.c
> ===================================================================
> --- mmotm-0303.orig/mm/memcontrol.c
> +++ mmotm-0303/mm/memcontrol.c
> @@ -926,13 +926,12 @@ void mem_cgroup_add_lru_list(struct page
>  }
>  
>  /*
> - * At handling SwapCache, pc->mem_cgroup may be changed while it's linked to
> - * lru because the page may.be reused after it's fully uncharged (because of
> - * SwapCache behavior).To handle that, unlink page_cgroup from LRU when charge
> - * it again. This function is only used to charge SwapCache. It's done under
> - * lock_page and expected that zone->lru_lock is never held.
> + * At handling SwapCache and other FUSE stuff, pc->mem_cgroup may be changed
> + * while it's linked to lru because the page may be reused after it's fully
> + * uncharged. To handle that, unlink page_cgroup from LRU when charge it again.
> + * It's done under lock_page and expected that zone->lru_lock isnever held.
>   */
> -static void mem_cgroup_lru_del_before_commit_swapcache(struct page *page)
> +static void mem_cgroup_lru_del_before_commit(struct page *page)
>  {
>  	unsigned long flags;
>  	struct zone *zone = page_zone(page);
> @@ -948,7 +947,7 @@ static void mem_cgroup_lru_del_before_co
>  	spin_unlock_irqrestore(&zone->lru_lock, flags);
>  }
>  
> -static void mem_cgroup_lru_add_after_commit_swapcache(struct page *page)
> +static void mem_cgroup_lru_add_after_commit(struct page *page)
>  {
>  	unsigned long flags;
>  	struct zone *zone = page_zone(page);
> @@ -2428,7 +2427,7 @@ int mem_cgroup_newpage_charge(struct pag
>  }
>  
>  static void
> -__mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr,
> +__mem_cgroup_commit_charge_lrucare(struct page *page, struct mem_cgroup *ptr,
>  					enum charge_type ctype);
>  
>  int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
> @@ -2468,17 +2467,22 @@ int mem_cgroup_cache_charge(struct page 
>  	if (unlikely(!mm))
>  		mm = &init_mm;
>  
> -	if (page_is_file_cache(page))
> -		return mem_cgroup_charge_common(page, mm, gfp_mask,
> +	if (page_is_file_cache(page) && !PageLRU(page)) {
> +		ret = mem_cgroup_charge_common(page, mm, gfp_mask,
>  				MEM_CGROUP_CHARGE_TYPE_CACHE);
> -
> -	/* shmem */
> -	if (PageSwapCache(page)) {
> +	} else if (page_is_file_cache(page)) {
> +		struct mem_cgroup *mem;
> +		/* Page on LRU should be moved to the _new_ LRU */
> +		ret = __mem_cgroup_try_charge(mm, gfp_mask, 1, &mem, true);
> +		if (!ret)
> +			__mem_cgroup_commit_charge_lrucare(page, mem,
> +					MEM_CGROUP_CHARGE_TYPE_CACHE);
> +	} else if (PageSwapCache(page)) {
>  		struct mem_cgroup *mem;
> -
>  		ret = mem_cgroup_try_charge_swapin(mm, page, gfp_mask, &mem);
> +
>  		if (!ret)
> -			__mem_cgroup_commit_charge_swapin(page, mem,
> +			__mem_cgroup_commit_charge_lrucare(page, mem,
>  					MEM_CGROUP_CHARGE_TYPE_SHMEM);
>  	} else
>  		ret = mem_cgroup_charge_common(page, mm, gfp_mask,
> @@ -2529,7 +2533,7 @@ charge_cur_mm:
>  }
>  
>  static void
> -__mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr,
> +__mem_cgroup_commit_charge_lrucare(struct page *page, struct mem_cgroup *ptr,
>  					enum charge_type ctype)
>  {
>  	struct page_cgroup *pc;
> @@ -2540,9 +2544,9 @@ __mem_cgroup_commit_charge_swapin(struct
>  		return;
>  	cgroup_exclude_rmdir(&ptr->css);
>  	pc = lookup_page_cgroup(page);
> -	mem_cgroup_lru_del_before_commit_swapcache(page);
> +	mem_cgroup_lru_del_before_commit(page);
>  	__mem_cgroup_commit_charge(ptr, page, 1, pc, ctype);
> -	mem_cgroup_lru_add_after_commit_swapcache(page);
> +	mem_cgroup_lru_add_after_commit(page);
>  	/*
>  	 * Now swap is on-memory. This means this page may be
>  	 * counted both as mem and swap....double count.
> @@ -2580,7 +2584,7 @@ __mem_cgroup_commit_charge_swapin(struct
>  
>  void mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr)
>  {
> -	__mem_cgroup_commit_charge_swapin(page, ptr,
> +	__mem_cgroup_commit_charge_lrucare(page, ptr,
>  					MEM_CGROUP_CHARGE_TYPE_MAPPED);
>  }
>  
> 

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^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [PATCH] memcg: fix to leave pages on wrong LRU with FUSE.
  2011-03-08  0:59 ` Daisuke Nishimura
@ 2011-03-08  1:02   ` KAMEZAWA Hiroyuki
  2011-03-08  2:04     ` Daisuke Nishimura
  0 siblings, 1 reply; 5+ messages in thread
From: KAMEZAWA Hiroyuki @ 2011-03-08  1:02 UTC (permalink / raw)
  To: Daisuke Nishimura; +Cc: linux-mm, balbir, akpm, miklos

On Tue, 8 Mar 2011 09:59:39 +0900
Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:

> On Mon, 7 Mar 2011 15:00:49 +0900
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> 
> > At this point, I'm not sure this is a fix for 
> >    https://bugzilla.kernel.org/show_bug.cgi?id=30432.
> > 
> > The behavior seems very similar to SwapCache case and this is a possible
> > bug and this patch can be a fix. Nishimura-san, how do you think ?
> > 
> As long as I can read the source code, I also think this is a possible bug.
> 
> > But I'm not sure how to test this....please review.
> > 
> > =
> > fs/fuse/dev.c::fuse_try_move_page() does
> > 
> >    (1) remove a page from page cache by ->steal()
> >    (2) re-add the page to page cache 
> >    (3) link the page to LRU if it was _not_ on LRU at (1)
> > 
> > 
> > This implies the page can be _on_ LRU when add_to_page_cache_locked() is called.
> > So, the page is added to a memory cgroup while it's on LRU.
> > 
> > This is the same behavior as SwapCache, 'newly charged pages may be on LRU'
> > and needs special care as
> >  - remove page from old memcg's LRU before overwrite pc->mem_cgroup.
> >  - add page to new memcg's LRU after overwrite pc->mem_cgroup.
> > 
> > So, reusing SwapCache code with renaming for fix.
> > 
> > Note: a page on pagevec(LRU).
> > 
> > If a page is not PageLRU(page) but on pagevec(LRU), it may be added to LRU
> > while we overwrite page->mapping. But in that case, PCG_USED bit of
> > the page_cgroup is not set and the page_cgroup will not be added to
> > wrong memcg's LRU. So, this patch's logic will work fine.
> > (It has been tested with SwapCache.)
> > 
> As for SwapCache, mem_cgroup_lru_add_after_commit() will be allways called,
> and it will link the page to LRU. But, if I read this patch correctly,
> a page cache on pagevec may not be added to a *proper* memcg's LRU.
> 
>       lru_add_drain()           mem_cgroup_cache_charge()
>   ----------------------------------------------------------
>                                   if (!PageLRU())
>     SetPageLRU()
>     add_page_to_lru_list()
>       mem_cgroup_add_lru_list()
>       -> do nothing
>                                     mem_cgroup_charge_common()
>                                       mem_cgroup_commit_charge()
>                                       -> set PCG_USED
> 

Hmm, yes, that's possible case.

So, PageLRU() && !PcgAcctLru(pc) should be checked after commit ?

I think we can add optimization later (add per-memcg-lru-pegecgrou-vec or some)


Thanks,
-Kame

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^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [PATCH] memcg: fix to leave pages on wrong LRU with FUSE.
  2011-03-08  1:02   ` KAMEZAWA Hiroyuki
@ 2011-03-08  2:04     ` Daisuke Nishimura
  2011-03-08  2:06       ` KAMEZAWA Hiroyuki
  0 siblings, 1 reply; 5+ messages in thread
From: Daisuke Nishimura @ 2011-03-08  2:04 UTC (permalink / raw)
  To: KAMEZAWA Hiroyuki; +Cc: linux-mm, balbir, akpm, miklos, Daisuke Nishimura

On Tue, 8 Mar 2011 10:02:42 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:

> On Tue, 8 Mar 2011 09:59:39 +0900
> Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:
> 
> > On Mon, 7 Mar 2011 15:00:49 +0900
> > KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> > 
> > > At this point, I'm not sure this is a fix for 
> > >    https://bugzilla.kernel.org/show_bug.cgi?id=30432.
> > > 
> > > The behavior seems very similar to SwapCache case and this is a possible
> > > bug and this patch can be a fix. Nishimura-san, how do you think ?
> > > 
> > As long as I can read the source code, I also think this is a possible bug.
> > 
> > > But I'm not sure how to test this....please review.
> > > 
> > > =
> > > fs/fuse/dev.c::fuse_try_move_page() does
> > > 
> > >    (1) remove a page from page cache by ->steal()
> > >    (2) re-add the page to page cache 
> > >    (3) link the page to LRU if it was _not_ on LRU at (1)
> > > 
> > > 
> > > This implies the page can be _on_ LRU when add_to_page_cache_locked() is called.
> > > So, the page is added to a memory cgroup while it's on LRU.
> > > 
> > > This is the same behavior as SwapCache, 'newly charged pages may be on LRU'
> > > and needs special care as
> > >  - remove page from old memcg's LRU before overwrite pc->mem_cgroup.
> > >  - add page to new memcg's LRU after overwrite pc->mem_cgroup.
> > > 
> > > So, reusing SwapCache code with renaming for fix.
> > > 
> > > Note: a page on pagevec(LRU).
> > > 
> > > If a page is not PageLRU(page) but on pagevec(LRU), it may be added to LRU
> > > while we overwrite page->mapping. But in that case, PCG_USED bit of
> > > the page_cgroup is not set and the page_cgroup will not be added to
> > > wrong memcg's LRU. So, this patch's logic will work fine.
> > > (It has been tested with SwapCache.)
> > > 
> > As for SwapCache, mem_cgroup_lru_add_after_commit() will be allways called,
> > and it will link the page to LRU. But, if I read this patch correctly,
> > a page cache on pagevec may not be added to a *proper* memcg's LRU.
> > 
> >       lru_add_drain()           mem_cgroup_cache_charge()
> >   ----------------------------------------------------------
> >                                   if (!PageLRU())
> >     SetPageLRU()
> >     add_page_to_lru_list()
> >       mem_cgroup_add_lru_list()
> >       -> do nothing
> >                                     mem_cgroup_charge_common()
> >                                       mem_cgroup_commit_charge()
> >                                       -> set PCG_USED
> > 
> 
> Hmm, yes, that's possible case.
> 
> So, PageLRU() && !PcgAcctLru(pc) should be checked after commit ?
> 
I think so, as mem_cgroup_lru_add_after_commit() does.

> I think we can add optimization later (add per-memcg-lru-pegecgrou-vec or some)
> 
In current mmotm, fuse uses replace_page_cache(), which uses mem_cgroup_(prepare|end)_migration(),
so I think we can handle this problem in a different way instead of changing
mem_cgroup_cache_charge(), which I think is a fast-path operation.

Thanks,
Daisuke Nishimura.

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^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [PATCH] memcg: fix to leave pages on wrong LRU with FUSE.
  2011-03-08  2:04     ` Daisuke Nishimura
@ 2011-03-08  2:06       ` KAMEZAWA Hiroyuki
  0 siblings, 0 replies; 5+ messages in thread
From: KAMEZAWA Hiroyuki @ 2011-03-08  2:06 UTC (permalink / raw)
  To: Daisuke Nishimura; +Cc: linux-mm, balbir, akpm, miklos

On Tue, 8 Mar 2011 11:04:43 +0900
Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:

> On Tue, 8 Mar 2011 10:02:42 +0900
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> 
> > On Tue, 8 Mar 2011 09:59:39 +0900
> > Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:
> > 
> > > On Mon, 7 Mar 2011 15:00:49 +0900
> > > KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> > > 
> > > > At this point, I'm not sure this is a fix for 
> > > >    https://bugzilla.kernel.org/show_bug.cgi?id=30432.
> > > > 
> > > > The behavior seems very similar to SwapCache case and this is a possible
> > > > bug and this patch can be a fix. Nishimura-san, how do you think ?
> > > > 
> > > As long as I can read the source code, I also think this is a possible bug.
> > > 
> > > > But I'm not sure how to test this....please review.
> > > > 
> > > > =
> > > > fs/fuse/dev.c::fuse_try_move_page() does
> > > > 
> > > >    (1) remove a page from page cache by ->steal()
> > > >    (2) re-add the page to page cache 
> > > >    (3) link the page to LRU if it was _not_ on LRU at (1)
> > > > 
> > > > 
> > > > This implies the page can be _on_ LRU when add_to_page_cache_locked() is called.
> > > > So, the page is added to a memory cgroup while it's on LRU.
> > > > 
> > > > This is the same behavior as SwapCache, 'newly charged pages may be on LRU'
> > > > and needs special care as
> > > >  - remove page from old memcg's LRU before overwrite pc->mem_cgroup.
> > > >  - add page to new memcg's LRU after overwrite pc->mem_cgroup.
> > > > 
> > > > So, reusing SwapCache code with renaming for fix.
> > > > 
> > > > Note: a page on pagevec(LRU).
> > > > 
> > > > If a page is not PageLRU(page) but on pagevec(LRU), it may be added to LRU
> > > > while we overwrite page->mapping. But in that case, PCG_USED bit of
> > > > the page_cgroup is not set and the page_cgroup will not be added to
> > > > wrong memcg's LRU. So, this patch's logic will work fine.
> > > > (It has been tested with SwapCache.)
> > > > 
> > > As for SwapCache, mem_cgroup_lru_add_after_commit() will be allways called,
> > > and it will link the page to LRU. But, if I read this patch correctly,
> > > a page cache on pagevec may not be added to a *proper* memcg's LRU.
> > > 
> > >       lru_add_drain()           mem_cgroup_cache_charge()
> > >   ----------------------------------------------------------
> > >                                   if (!PageLRU())
> > >     SetPageLRU()
> > >     add_page_to_lru_list()
> > >       mem_cgroup_add_lru_list()
> > >       -> do nothing
> > >                                     mem_cgroup_charge_common()
> > >                                       mem_cgroup_commit_charge()
> > >                                       -> set PCG_USED
> > > 
> > 
> > Hmm, yes, that's possible case.
> > 
> > So, PageLRU() && !PcgAcctLru(pc) should be checked after commit ?
> > 
> I think so, as mem_cgroup_lru_add_after_commit() does.
> 
> > I think we can add optimization later (add per-memcg-lru-pegecgrou-vec or some)
> > 
> In current mmotm, fuse uses replace_page_cache(), which uses mem_cgroup_(prepare|end)_migration(),
> so I think we can handle this problem in a different way instead of changing
> mem_cgroup_cache_charge(), which I think is a fast-path operation.
> 

Hmm, but a fix for 2.6.37 is a problem... _AND_ this kind of breakage by
some code can be happen, again. I think we need a check in this path.
Let's try and see overheads.

Thanks,
-Kame

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^ permalink raw reply	[flat|nested] 5+ messages in thread

end of thread, other threads:[~2011-03-08  2:12 UTC | newest]

Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2011-03-07  6:00 [PATCH] memcg: fix to leave pages on wrong LRU with FUSE KAMEZAWA Hiroyuki
2011-03-08  0:59 ` Daisuke Nishimura
2011-03-08  1:02   ` KAMEZAWA Hiroyuki
2011-03-08  2:04     ` Daisuke Nishimura
2011-03-08  2:06       ` KAMEZAWA Hiroyuki

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