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AJvYcCVRMQsTr+Yo5EYKJLeOou3GuPozs65yt4vlN/mhHSIgQsJmrOrT80npbqk2swGjbwPVhQn+1BHulciu2pzIv3RjKOI= X-Gm-Message-State: AOJu0YyX0sS8NbsNRfaUmSrIcOmrds3HuDtl3ZqGXbB0N0U/oWNvsi5A Y1IPJZ1wjNIE+ds9SQc7KzfPTvC5evD+k09JhJPmK/2t43wzb+4+goGgh63C0de1HeN2ClbeZHE f2Uz/7wF3AVpL+hbgij7AFJ5o+Og= X-Google-Smtp-Source: AGHT+IHPzGgeVebYi5e5XGY212SUvxo7txV8bzERYstCFCs9yobH6mfd8vu3+8VNXVU7DnbhLkANMq/J4WzIHMCFe4A= X-Received: by 2002:a81:9a47:0:b0:607:57c5:41fc with SMTP id r68-20020a819a47000000b0060757c541fcmr18443898ywg.15.1708536942761; Wed, 21 Feb 2024 09:35:42 -0800 (PST) MIME-Version: 1.0 References: <20240221085036.105621-1-21cnbao@gmail.com> In-Reply-To: <20240221085036.105621-1-21cnbao@gmail.com> From: Vishal Moola Date: Wed, 21 Feb 2024 09:35:31 -0800 Message-ID: Subject: Re: [PATCH] madvise:madvise_cold_or_pageout_pte_range(): allow split while folio_estimated_sharers = 0 To: Barry Song <21cnbao@gmail.com> Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Barry Song , Yin Fengwei , Yu Zhao , Ryan Roberts , David Hildenbrand , Kefeng Wang , Matthew Wilcox , Minchan Kim , Yang Shi Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Stat-Signature: ymc8d3crpb8cyg48qqsx4a8k37o9rmgo X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: AFE7A4001B X-HE-Tag: 1708536943-64784 X-HE-Meta: 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 +/E+2OQH 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Feb 21, 2024 at 12:50=E2=80=AFAM Barry Song <21cnbao@gmail.com> wro= te: > > From: Barry Song > > The purpose is stopping splitting large folios whose mapcount are 2 or > above. Folios whose estimated_shares =3D 0 should be still perfect and > even better candidates than estimated_shares =3D 1. > > Consider a pte-mapped large folio with 16 subpages, if we unmap 1-15, > the current code will split folios and reclaim them while madvise goes > on this folio; but if we unmap subpage 0, we will keep this folio and > break. This is weird. > For pmd-mapped large folios, we can still use "=3D 1" as the condition > as anyway we have the entire map for it. So this patch doesn't change > the condition for pmd-mapped large folios. > This also explains why we had been using "=3D 1" for both pmd-mapped and > pte-mapped large folios before commit 07e8c82b5eff ("madvise: convert > madvise_cold_or_pageout_pte_range() to use folios"), because in the > past, we used the mapcount of the specific subpage, since the subpage > had pte present, its mapcount wouldn't be 0. > The problem can be quite easily reproduced by writing a small program, > unmapping the first subpage of a pte-mapped large folio vs. unmapping > anyone other than the first subpage. > > Fixes: 2f406263e3e9 ("madvise:madvise_cold_or_pageout_pte_range(): don't = use mapcount() against large folio for sharing check") > Cc: Yin Fengwei > Cc: Yu Zhao > Cc: Ryan Roberts > Cc: David Hildenbrand > Cc: Kefeng Wang > Cc: Matthew Wilcox > Cc: Minchan Kim > Cc: Vishal Moola (Oracle) > Cc: Yang Shi > Signed-off-by: Barry Song Reviewed-by: Vishal Moola (Oracle) > --- > mm/madvise.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/madvise.c b/mm/madvise.c > index cfa5e7288261..abde3edb04f0 100644 > --- a/mm/madvise.c > +++ b/mm/madvise.c > @@ -453,7 +453,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *p= md, > if (folio_test_large(folio)) { > int err; > > - if (folio_estimated_sharers(folio) !=3D 1) > + if (folio_estimated_sharers(folio) > 1) > break; > if (pageout_anon_only_filter && !folio_test_anon(= folio)) > break; > -- > 2.34.1 >