mm: remove unneeded __meminit annotation

  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(-)
  

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.
  

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.
  

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.
  

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.