linux-kernel - Re: [PATCH] mm: split thp synchronously on MADV

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Date:   Tue, 23 Nov 2021 09:28:34 -0800
From:   Shakeel Butt <shakeelb@...gle.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Yang Shi <shy828301@...il.com>, Zi Yan <ziy@...dia.com>,
        Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: split thp synchronously on MADV_DONTNEED

On Tue, Nov 23, 2021 at 9:26 AM David Hildenbrand <david@...hat.com> wrote:
>
> On 23.11.21 18:24, Shakeel Butt wrote:
> > On Tue, Nov 23, 2021 at 9:20 AM David Hildenbrand <david@...hat.com> wrote:
> >>
> >> On 23.11.21 18:17, Shakeel Butt wrote:
> >>> On Tue, Nov 23, 2021 at 8:57 AM David Hildenbrand <david@...hat.com> wrote:
> >>>>
> >>> [...]
> >>>>>>
> >>>>>> I do wonder which these locking contexts are exactly, and if we could
> >>>>>> also do the same thing on ordinary munmap -- because I assume it can be
> >>>>>> similarly problematic for some applications.
> >>>>>
> >>>>> This is a good question regarding munmap. One main difference is
> >>>>> munmap takes mmap_lock in write mode and usually performance critical
> >>>>> applications avoid such operations.
> >>>>
> >>>> Maybe we can extend it too most page zapping, if that makes things simpler.
> >>>>
> >>>
> >>> Do you mean doing sync THP split for most of page zapping functions
> >>> (but only if that makes things simpler)?
> >>>
> >>
> >> Yes -- if there are no downsides.
> >>
> >
> > I will try. At the moment the assumption of "Not null zap_details
> > implies leave swap entries" is giving me a headache.
>
> Not only you, did you stumble over
>
> https://lkml.kernel.org/r/20211115134951.85286-1-peterx@redhat.com
>
> already?
>

Oh thanks for the pointer. I missed that. I will take a look. Thanks again.