linux-kernel - Re: [PATCH v2 3/6] mm/zsmalloc: use a proper page type

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Date: Tue, 25 Jun 2024 15:33:38 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: David Hildenbrand <david@...hat.com>
Cc: Matthew Wilcox <willy@...radead.org>, Sergey Senozhatsky
 <senozhatsky@...omium.org>, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, Mike Rapoport <rppt@...nel.org>, Minchan Kim
 <minchan@...nel.org>, Hyeonggon Yoo <42.hyeyoo@...il.com>
Subject: Re: [PATCH v2 3/6] mm/zsmalloc: use a proper page type

On Fri, 31 May 2024 16:32:04 +0200 David Hildenbrand <david@...hat.com> wrote:

> On 31.05.24 16:27, Matthew Wilcox wrote:
> > On Thu, May 30, 2024 at 02:01:23PM +0900, Sergey Senozhatsky wrote:
> >      1409:       83 c0 01                add    $0x1,%eax
> >                  if (mapcount < PAGE_MAPCOUNT_RESERVE + 1)
> >      140c:       83 f8 81                cmp    $0xffffff81,%eax
> >      140f:       7d 63                   jge    1474 <filemap_unaccount_folio+0x8
> > 4>
> >          if (folio_test_hugetlb(folio))
> >      1411:       80 7b 33 84             cmpb   $0x84,0x33(%rbx)
> >      1415:       74 4e                   je     1465 <filemap_unaccount_folio+0x75>
> > 
> > so we go from "mov, and, cmp, je" to just "cmpb, je", which must surely
> > be faster to execute as well as being more compact in the I$ (6 bytes vs 15).
> > 
> > Anyway, not tested but this is the patch I used to generate the above.
> > More for comment than application.
> 
> Right, it's likely very similar to my previous proposal to use 8 bit 
> (uint8_t) for the type.
> 
> https://lore.kernel.org/all/00ba1dff-7c05-46e8-b0d9-a78ac1cfc198@redhat.com/
> 
> I would prefer if we would do that separately; unless someone is able to 
> raise why we care about zram + 256KiB that much right now. (claim: we don't)
> 

iow, "this is ok for now", yes?

I'd like to push this into mm-"stable" later this week.  Speak now or
forever hold your pieces.