linux-kernel - Re: [PATCH] mm: remove unneeded _

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Date:   Tue, 8 Aug 2023 04:16:57 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: remove unneeded __meminit annotation

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.