linux-kernel - Re: [PATCH 2/2] mm/damon/vaddr: remove comparison between mm and last

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Date:   Sat, 27 Aug 2022 05:06:12 +0800
From:   Kaixu Xia <xiakaixu1987@...il.com>
To:     SeongJae Park <sj@...nel.org>
Cc:     akpm@...ux-foundation.org, damon@...ts.linux.dev,
        linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>,
        Kaixu Xia <kaixuxia@...cent.com>
Subject: Re: [PATCH 2/2] mm/damon/vaddr: remove comparison between mm and
 last_mm when checking region accesses

On Sat, Aug 27, 2022 at 1:16 AM SeongJae Park <sj@...nel.org> wrote:
>
> Hi Kaixu,
>
> On Fri, 26 Aug 2022 16:31:18 +0800 xiakaixu1987@...il.com wrote:
>
> > From: Kaixu Xia <kaixuxia@...cent.com>
> >
> > The damon regions that belong to the same damon target have the same
> > 'struct mm_struct *mm', so it's unnecessary to compare the mm and last_mm
> > objects among the damon regions in one damon target when checking accesses.
>
> There could be multiple targets, and 'damon_va_check_accesses()' calls
> '__damon_va_check_accesses()' for all the targets.  However,
> 'damon_va_check_accesses()' doesn't note if '__damon_va_check_accesses()' is
> called with a target that same to the target it was called with for the last
> time.  Hence the check is necessary.

There could be many regions(1000 max limit) in one target and the mm
is same within
the target, maybe we don't need to maintain the 'last_mm' and do the
check every time
when the target is same.
But yes, the check is necessary when the target changed in
'__damon_va_check_accesses()',
this RFC patch missed this case :)  will fix it.

>
> If I'm missing something, please let me know.
>
>
> Thanks,
> SJ
>
> [...]