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Date: Tue, 8 Aug 2023 04:26:48 +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 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.
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