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Mon, 23 Mar 2026 10:43:49 -0700 (PDT) MIME-Version: 1.0 References: <20260322070843.941997-1-surenb@google.com> <65cb38ee-2815-4b11-929d-3fc1528cc620@lucifer.local> In-Reply-To: From: Suren Baghdasaryan Date: Mon, 23 Mar 2026 10:43:38 -0700 X-Gm-Features: AQROBzATssHfmB3mILFMH-ju4s8zMXclEpaPQfAhXS_N2eL0otFup8_0lBG6AY4 Message-ID: Subject: Re: [PATCH 1/1] mm/vmscan: prevent MGLRU reclaim from pinning address space To: "Lorenzo Stoakes (Oracle)" Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, david@kernel.org, mhocko@kernel.org, zhengqi.arch@bytedance.com, yuzhao@google.com, shakeel.butt@linux.dev, willy@infradead.org, Liam.Howlett@oracle.com, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 9F44AA0016 X-Stat-Signature: cruw8ggi61khnzogbjakk3ztr3ygi197 X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1774287831-160549 X-HE-Meta: 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 aq3dKUVq RiRRYi3lLSXy1pYSkgokcNyhOvXnolr2dc74xohYtkWvPXmHodkF33gBfojgepx2rFZdGwkqpHRcwLppahrTp/YEOgQAK8KUi4rbIB59B5nViF4JLVvERrLsvh2DbfQSqyS/vuTPJGJDh+/A75f/BsO+tgCFw8VGTvPmiSgZTUuwqItZMrXfbsincjodtJLATd1xqWDGVF8YL8AYRGV5H2z54qJJxQYNTtJCXU51qoMg2mdIvdmsi2krB9rUxP0k1IAaTZcrDSg3KkNyY1XLlcSZjvFna5Rn0dnEXcPBURmPe8IM6eiNwCYy6Xw0Mb899tHea5eO9iaOf85GSrBctBqynRg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Mar 23, 2026 at 10:02=E2=80=AFAM Lorenzo Stoakes (Oracle) wrote: > > On Mon, Mar 23, 2026 at 09:26:02AM -0700, Suren Baghdasaryan wrote: > > On Mon, Mar 23, 2026 at 6:43=E2=80=AFAM Lorenzo Stoakes (Oracle) wrote: > > > > > > On Sun, Mar 22, 2026 at 12:08:43AM -0700, Suren Baghdasaryan wrote: > > > > When shrinking lruvec, MGLRU pins address space before walking it. > > > > This is excessive since all it needs for walking the page range is > > > > a stable mm_struct to be able to take and release mmap_read_lock an= d > > > > a stable mm->mm_mt tree to walk. This address space pinning results > > > > in delays when releasing the memory of a dying process. This also > > > > prevents mm reapers (both in-kernel oom-reaper and userspace > > > > process_mrelease()) from doing their job during MGLRU scan because > > > > they check task_will_free_mem() which will yield negative result du= e > > > > to the elevated mm->mm_users. > > > > > > > > Replace unnecessary address space pinning with mm_struct pinning by > > > > replacing mmget/mmput with mmgrab/mmdrop calls. mm_mt is contained > > > > within mm_struct itself, therefore it won't be freed as long as > > > > mm_struct is stable and it won't change during the walk because > > > > mmap_read_lock is being held. > > > > > > > > Fixes: bd74fdaea146 ("mm: multi-gen LRU: support page table walks") > > > > Signed-off-by: Suren Baghdasaryan > > > > > > Oh and sorry, missed this - do we need a 'Fixed' for something that's= just a > > > perf improvement? > > > > > > This doesn't seem buggy? > > > > Well, if we are pinning something we should not is that a bug? I > > didn't CC stable, so I don't expect it to be backported (though if > > it's accepted, we will backport it in Android as it causes real > > problems with reclaim), however if someone is looking for MGLRU fixes > > I would like this patch to be discoverable. If you feel strongly about > > it, I'll remove the tag. > > I don't feel that strongly about it :>) > > > > > Thanks for the review! > > No problem! Working through your vma killable series atm also :) Thanks! I will need to respin v5 after Sashiko found a couple of legit issues at [1] but I'll wait for you to post your feedback before sending it. [1] https://sashiko.dev/#/patchset/20260322054309.898214-1-surenb@google.co= m > > > > > > > > > Thanks, Lorenzo > > Cheers, Lorenzo