linux-kernel - Re: [PATCH AUTOSEL 13/14] mm/thp: ClearPageDoubleMap in first page_add_file

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Date:   Thu, 28 Apr 2022 22:45:18 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Hugh Dickins <hughd@...gle.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, linux-kernel@...r.kernel.org,
        Yang Shi <shy828301@...il.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-mm@...ck.org, Sasha Levin <sashal@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH AUTOSEL 13/14] mm/thp: ClearPageDoubleMap in first
 page_add_file_rmap()

+Sasha and Paolo

On Thu, Apr 28, 2022, Hugh Dickins wrote:
> On Thu, 28 Apr 2022, Greg Kroah-Hartman wrote:
> > On Thu, Apr 28, 2022 at 09:51:58AM -0700, Hugh Dickins wrote:
> > > On Thu, 28 Apr 2022, Greg Kroah-Hartman wrote:
> > > 
> > > > From: Hugh Dickins <hughd@...gle.com>
> > > > 
> > > > commit bd55b0c2d64e84a75575f548a33a3dfecc135b65 upstream.
> > > > 
> > > > PageDoubleMap is maintained differently for anon and for shmem+file: the
> > > > shmem+file one was never cleared, because a safe place to do so could
> > > > not be found; so it would blight future use of the cached hugepage until
> > > > evicted.
> > > > 
> > > > See https://lore.kernel.org/lkml/1571938066-29031-1-git-send-email-yang.shi@linux.alibaba.com/
> > > > 
> > > > But page_add_file_rmap() does provide a safe place to do so (though later
> > > > than one might wish): allowing testing to return to an initial state
> > > > without a damaging drop_caches.
> > > > 
> > > > Link: https://lkml.kernel.org/r/61c5cf99-a962-9a25-597a-53ab1bd8fbc0@google.com
> > > > Fixes: 9a73f61bdb8a ("thp, mlock: do not mlock PTE-mapped file huge pages")
> > > > Signed-off-by: Hugh Dickins <hughd@...gle.com>
> > > > Reviewed-by: Yang Shi <shy828301@...il.com>
> > > > Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> > > > Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> > > > Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
> > > > Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > > 
> > > NAK.
> > > 
> > > I thought we had a long-standing agreement that AUTOSEL does not try
> > > to add patches from akpm's tree which had not been marked for stable.
> > 
> > True, this was my attempt at saying "hey these all look like they should
> > go to stable trees, why not?"
> 
> Okay, it seems I should have read "AUTOSEL" as "Hey, GregKH here,
> these all look like they should go to stable trees, why not?",
> which would have drawn a friendlier response.

FWIW, Sasha has been using MANUALSEL for the KVM tree to solicit an explicit ACK
from Paolo for these types of patches.  AFAICT, it has been working quite well.