[PATCH] mm: remove unneeded __meminit annotation

[PATCH] mm: remove unneeded __meminit annotation

[Miaohe Lin]

kswapd_stop() and kcompactd_stop() are only called when MEMORY_HOTREMOVE
is enabled. So wrap them under CONFIG_MEMORY_HOTREMOVE and further remove
__meminit annotation. No functional change intended.

Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
---
 include/linux/compaction.h | 2 +-
 include/linux/swap.h       | 2 +-
 mm/compaction.c            | 4 +++-
 mm/vmscan.c                | 4 +++-
 4 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/include/linux/compaction.h b/include/linux/compaction.h
index e94776496049..3dbb7eea96eb 100644
--- a/include/linux/compaction.h
+++ b/include/linux/compaction.h
@@ -99,7 +99,7 @@ bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
 					int alloc_flags);
 
 extern void __meminit kcompactd_run(int nid);
-extern void __meminit kcompactd_stop(int nid);
+extern void kcompactd_stop(int nid);
 extern void wakeup_kcompactd(pg_data_t *pgdat, int order, int highest_zoneidx);
 
 #else
diff --git a/include/linux/swap.h b/include/linux/swap.h
index bb5adc604144..c102587b3a86 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -437,7 +437,7 @@ static inline bool node_reclaim_enabled(void)
 void check_move_unevictable_folios(struct folio_batch *fbatch);
 
 extern void __meminit kswapd_run(int nid);
-extern void __meminit kswapd_stop(int nid);
+extern void kswapd_stop(int nid);
 
 #ifdef CONFIG_SWAP
 
diff --git a/mm/compaction.c b/mm/compaction.c
index ea61922a1619..c59244d2ed5a 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -3132,11 +3132,12 @@ void __meminit kcompactd_run(int nid)
 	}
 }
 
+#ifdef CONFIG_MEMORY_HOTREMOVE
 /*
  * Called by memory hotplug when all memory in a node is offlined. Caller must
  * be holding mem_hotplug_begin/done().
  */
-void __meminit kcompactd_stop(int nid)
+void kcompactd_stop(int nid)
 {
 	struct task_struct *kcompactd = NODE_DATA(nid)->kcompactd;
 
@@ -3145,6 +3146,7 @@ void __meminit kcompactd_stop(int nid)
 		NODE_DATA(nid)->kcompactd = NULL;
 	}
 }
+#endif
 
 /*
  * It's optimal to keep kcompactd on the same CPUs as their memory, but
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 80e9a222e522..eb4db273bf7e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -7897,11 +7897,12 @@ void __meminit kswapd_run(int nid)
 	pgdat_kswapd_unlock(pgdat);
 }
 
+#ifdef CONFIG_MEMORY_HOTREMOVE
 /*
  * Called by memory hotplug when all memory in a node is offlined.  Caller must
  * be holding mem_hotplug_begin/done().
  */
-void __meminit kswapd_stop(int nid)
+void kswapd_stop(int nid)
 {
 	pg_data_t *pgdat = NODE_DATA(nid);
 	struct task_struct *kswapd;
@@ -7914,6 +7915,7 @@ void __meminit kswapd_stop(int nid)
 	}
 	pgdat_kswapd_unlock(pgdat);
 }
+#endif
 
 static int __init kswapd_init(void)
 {
-- 
2.33.0

Re: [PATCH] mm: remove unneeded __meminit annotation

[Matthew Wilcox]

On Tue, Aug 08, 2023 at 09:58:31AM +0800, Miaohe Lin wrote:
> kswapd_stop() and kcompactd_stop() are only called when MEMORY_HOTREMOVE
> is enabled. So wrap them under CONFIG_MEMORY_HOTREMOVE and further remove
> __meminit annotation. No functional change intended.

I don't understand why this is an improvement.  If CONFIG_MEMORY_HOTREMOVE
is disabled, the linker drops this section (... right?)  If it's enabled,
then it gets shunted off into a cold section.  So it seems like this
patch strictly makes things worse.  But maybe I misunderstood.

Re: [PATCH] mm: remove unneeded __meminit annotation

[Miaohe Lin]

On 2023/8/8 10:31, Matthew Wilcox wrote:
> On Tue, Aug 08, 2023 at 09:58:31AM +0800, Miaohe Lin wrote:
>> kswapd_stop() and kcompactd_stop() are only called when MEMORY_HOTREMOVE
>> is enabled. So wrap them under CONFIG_MEMORY_HOTREMOVE and further remove
>> __meminit annotation. No functional change intended.
> 
> I don't understand why this is an improvement.  If CONFIG_MEMORY_HOTREMOVE
> is disabled, the linker drops this section (... right?)  If it's enabled,

When CONFIG_MEMORY_HOTREMOVE is disabled, without this patch:

size mm/compaction.o
   text	   data	    bss	    dec	    hex	filename
 103164	  30873	      0	 134037	  20b95	mm/compaction.o

size mm/vmscan.o
   text	   data	    bss	    dec	    hex	filename
 158775	  49612	     64	 208451	  32e43	mm/vmscan.o

while with this patch:

size mm/compaction.o
   text	   data	    bss	    dec	    hex	filename
 102915	  30865	      0	 133780	  20a94	mm/compaction.o

size mm/vmscan.o
   text	   data	    bss	    dec	    hex	filename
 158534	  49604	     64	 208202	  32d4a	mm/vmscan.o

We can reduce each .o by ~250 bytes.

> then it gets shunted off into a cold section.  So it seems like this
> patch strictly makes things worse.  But maybe I misunderstood.

What about add __cold annotation? Something like:

diff --git a/mm/vmscan.c b/mm/vmscan.c
index eb4db273bf7e..e27ffa22c70f 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -7902,7 +7902,7 @@ void __meminit kswapd_run(int nid)
  * Called by memory hotplug when all memory in a node is offlined.  Caller must
  * be holding mem_hotplug_begin/done().
  */
-void kswapd_stop(int nid)
+void __cold kswapd_stop(int nid)
 {
        pg_data_t *pgdat = NODE_DATA(nid);
        struct task_struct *kswapd;

Thanks.

Re: [PATCH] mm: remove unneeded __meminit annotation

[Matthew Wilcox]

On Tue, Aug 08, 2023 at 11:08:36AM +0800, Miaohe Lin wrote:
> On 2023/8/8 10:31, Matthew Wilcox wrote:
> > On Tue, Aug 08, 2023 at 09:58:31AM +0800, Miaohe Lin wrote:
> >> kswapd_stop() and kcompactd_stop() are only called when MEMORY_HOTREMOVE
> >> is enabled. So wrap them under CONFIG_MEMORY_HOTREMOVE and further remove
> >> __meminit annotation. No functional change intended.
> > 
> > I don't understand why this is an improvement.  If CONFIG_MEMORY_HOTREMOVE
> > is disabled, the linker drops this section (... right?)  If it's enabled,
> 
> When CONFIG_MEMORY_HOTREMOVE is disabled, without this patch:
> 
> size mm/compaction.o
>    text	   data	    bss	    dec	    hex	filename
>  103164	  30873	      0	 134037	  20b95	mm/compaction.o
> 
> size mm/vmscan.o
>    text	   data	    bss	    dec	    hex	filename
>  158775	  49612	     64	 208451	  32e43	mm/vmscan.o
> 
> while with this patch:
> 
> size mm/compaction.o
>    text	   data	    bss	    dec	    hex	filename
>  102915	  30865	      0	 133780	  20a94	mm/compaction.o
> 
> size mm/vmscan.o
>    text	   data	    bss	    dec	    hex	filename
>  158534	  49604	     64	 208202	  32d4a	mm/vmscan.o
> 
> We can reduce each .o by ~250 bytes.

But this is before the linker step!  That will be where the meminit
sections get dropped.  Assuming they are; I haven't verified.  You need
to compare before/after of the vmlinux, not the individual .o files.

Re: [PATCH] mm: remove unneeded __meminit annotation

[Matthew Wilcox]

On Tue, Aug 08, 2023 at 04:16:57AM +0100, Matthew Wilcox wrote:
> On Tue, Aug 08, 2023 at 11:08:36AM +0800, Miaohe Lin wrote:
> > On 2023/8/8 10:31, Matthew Wilcox wrote:
> > > On Tue, Aug 08, 2023 at 09:58:31AM +0800, Miaohe Lin wrote:
> > >> kswapd_stop() and kcompactd_stop() are only called when MEMORY_HOTREMOVE
> > >> is enabled. So wrap them under CONFIG_MEMORY_HOTREMOVE and further remove
> > >> __meminit annotation. No functional change intended.
> > > 
> > > I don't understand why this is an improvement.  If CONFIG_MEMORY_HOTREMOVE
> > > is disabled, the linker drops this section (... right?)  If it's enabled,
> > 
> > When CONFIG_MEMORY_HOTREMOVE is disabled, without this patch:
> > 
> > size mm/compaction.o
> >    text	   data	    bss	    dec	    hex	filename
> >  103164	  30873	      0	 134037	  20b95	mm/compaction.o
> > 
> > size mm/vmscan.o
> >    text	   data	    bss	    dec	    hex	filename
> >  158775	  49612	     64	 208451	  32e43	mm/vmscan.o
> > 
> > while with this patch:
> > 
> > size mm/compaction.o
> >    text	   data	    bss	    dec	    hex	filename
> >  102915	  30865	      0	 133780	  20a94	mm/compaction.o
> > 
> > size mm/vmscan.o
> >    text	   data	    bss	    dec	    hex	filename
> >  158534	  49604	     64	 208202	  32d4a	mm/vmscan.o
> > 
> > We can reduce each .o by ~250 bytes.
> 
> But this is before the linker step!  That will be where the meminit
> sections get dropped.  Assuming they are; I haven't verified.  You need
> to compare before/after of the vmlinux, not the individual .o files.

Ah, found it:

#if defined(CONFIG_MEMORY_HOTPLUG)
#define MEM_KEEP(sec)    *(.mem##sec)
#define MEM_DISCARD(sec)
#else
#define MEM_KEEP(sec)
#define MEM_DISCARD(sec) *(.mem##sec)
#endif

in include/asm-generic/vmlinux.lds.h

So yeah, I think this patch is garbage.

Re: [PATCH] mm: remove unneeded __meminit annotation

[Miaohe Lin]

On 2023/8/8 11:26, Matthew Wilcox wrote:
> On Tue, Aug 08, 2023 at 04:16:57AM +0100, Matthew Wilcox wrote:
>> On Tue, Aug 08, 2023 at 11:08:36AM +0800, Miaohe Lin wrote:
>>> On 2023/8/8 10:31, Matthew Wilcox wrote:
>>>> On Tue, Aug 08, 2023 at 09:58:31AM +0800, Miaohe Lin wrote:
>>>>> kswapd_stop() and kcompactd_stop() are only called when MEMORY_HOTREMOVE
>>>>> is enabled. So wrap them under CONFIG_MEMORY_HOTREMOVE and further remove
>>>>> __meminit annotation. No functional change intended.
>>>>
>>>> I don't understand why this is an improvement.  If CONFIG_MEMORY_HOTREMOVE
>>>> is disabled, the linker drops this section (... right?)  If it's enabled,
>>>
>>> When CONFIG_MEMORY_HOTREMOVE is disabled, without this patch:
>>>
>>> size mm/compaction.o
>>>    text	   data	    bss	    dec	    hex	filename
>>>  103164	  30873	      0	 134037	  20b95	mm/compaction.o
>>>
>>> size mm/vmscan.o
>>>    text	   data	    bss	    dec	    hex	filename
>>>  158775	  49612	     64	 208451	  32e43	mm/vmscan.o
>>>
>>> while with this patch:
>>>
>>> size mm/compaction.o
>>>    text	   data	    bss	    dec	    hex	filename
>>>  102915	  30865	      0	 133780	  20a94	mm/compaction.o
>>>
>>> size mm/vmscan.o
>>>    text	   data	    bss	    dec	    hex	filename
>>>  158534	  49604	     64	 208202	  32d4a	mm/vmscan.o
>>>
>>> We can reduce each .o by ~250 bytes.
>>
>> But this is before the linker step!  That will be where the meminit
>> sections get dropped.  Assuming they are; I haven't verified.  You need
>> to compare before/after of the vmlinux, not the individual .o files.

When CONFIG_MEMORY_HOTREMOVE is disabled, without patch:

size vmlinux
   text	   data	    bss	    dec	    hex	filename
70648396	21668938	17985540	110302874	693169a	vmlinux

while with patch:

size vmlinux
   text	   data	    bss	    dec	    hex	filename
70648128	21668938	17985540	110302606	693158e	vmlinux

vmlinux is still reduced by 268 bytes.

> 
> Ah, found it:
> 
> #if defined(CONFIG_MEMORY_HOTPLUG)
> #define MEM_KEEP(sec)    *(.mem##sec)
> #define MEM_DISCARD(sec)
> #else
> #define MEM_KEEP(sec)
> #define MEM_DISCARD(sec) *(.mem##sec)
> #endif
> 
> in include/asm-generic/vmlinux.lds.h

When CONFIG_MEMORY_HOTREMOVE is disabled, without this patch, kswapd_stop() and kcompactd_stop()
are dropped after system init.

But no insist in this patch.

Thanks for your comment.