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Fri, 23 Feb 2024 20:38:10 -0800 (PST) MIME-Version: 1.0 References: <20240223041550.77157-1-21cnbao@gmail.com> In-Reply-To: From: Barry Song <21cnbao@gmail.com> Date: Sat, 24 Feb 2024 12:37:59 +0800 Message-ID: Subject: Re: [PATCH RFC] mm: madvise: pageout: ignore references rather than clearing young To: Minchan Kim , sj@kernel.org Cc: akpm@linux-foundation.org, damon@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, mhocko@suse.com, hannes@cmpxchg.org, Barry Song Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 1BE05140005 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: cwg55rjawunwiqij1mfbkuef4k786s4o X-HE-Tag: 1708749491-281054 X-HE-Meta: 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 OUn8r3jY /DJmrsjZYs2LmmXnpldNI2ouiPunQ2S8L6tLih01vmFLspywhNymcfyRVSGD8QAPvyOnXmlk8GTKqzRuXphHJxTKOARO7JpVN2RwSqp6Ukoudjya8E3z96+tgvwkBCqZLiciFIHFsJ6AIA4RbuMEpanYl2LFIYRiEkCt2+O2L65ajD4s2KF8O4CIidzpZyLW2SpnUc2aRQ6eHgrbfv0R+d7k64naxQw5zv2eLKO7Ehb0w4WVKnOgLp1Asv8akWU/9uF+4KOodDRXzhgGA+3W8nkvv5EMli3ws7FJs/V0YpFzGMX4dSLadOb3nVWDqQeU3t1LXIjCcWfzJo/MDLNt3ETRy6eNrQDltzPfRobTLMe4JsFSWMFRZ6p4mHldn8kobEpsCjwzm8piROTZhGEWIS5SJTLvRmqrNk/7fpwSxY1130o9/tZmKe0XVV9KdP0csQu6mvJclaNVFUSGtZ9YTp1J7dQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000057, 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 Sat, Feb 24, 2024 at 7:24=E2=80=AFAM Minchan Kim wr= ote: > > On Sat, Feb 24, 2024 at 11:20:36AM +1300, Barry Song wrote: > > On Sat, Feb 24, 2024 at 11:09=E2=80=AFAM Minchan Kim wrote: > > > > > > Hi Barry, > > > > > > On Fri, Feb 23, 2024 at 05:15:50PM +1300, Barry Song wrote: > > > > From: Barry Song > > > > > > > > While doing MADV_PAGEOUT, the current code will clear PTE young > > > > so that vmscan won't read young flags to allow the reclamation > > > > of madvised folios to go ahead. > > > > > > Isn't it good to accelerate reclaiming? vmscan checks whether the > > > page was accessed recenlty by the young bit from pte and if it is, > > > it doesn't reclaim the page. Since we have cleared the young bit > > > in pte in madvise_pageout, vmscan is likely to reclaim the page > > > since it wouldn't see the ferencecd_ptes from folio_check_references. > > > > right, but the proposal is asking vmscan to skip the folio_check_refere= nces > > if this is a PAGEOUT. so we remove both pte_clear_young and rmap > > of folio_check_references. > > > > > > > > Could you clarify if I miss something here? > > > > guest you missed we are skipping folio_check_references now. > > we remove both, thus, make MADV_PAGEOUT 6% faster. > > This makes sense to me. > > Only concern was race with mlock during the reclaim but the race was alre= ady > there for normal page reclaming. Thus, mlock would already handle it. yes. in try_to_unmap_one(), mlock()'s vma is not reclaimed, while (page_vma_mapped_walk(&pvmw)) { /* Unexpected PMD-mapped THP? */ VM_BUG_ON_FOLIO(!pvmw.pte, folio); /* * If the folio is in an mlock()d vma, we must not swap it out. */ if (!(flags & TTU_IGNORE_MLOCK) && (vma->vm_flags & VM_LOCKED)) { /* Restore the mlock which got missed */ if (!folio_test_large(folio)) mlock_vma_folio(folio, vma); page_vma_mapped_walk_done(&pvmw); ret =3D false; break; } BTW=EF=BC=8C Hi SeongJae, I am not quite sure if damon also needs this, so I have kept damon as is by setting ignore_references =3D false. MADV_PAGEOUT is an explicit hint user= s don't want the memory to be reclaimed, I don't know if it is true for damon= as well. If you have some comments, please chime in. > > Thanks. Thanks Barry