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b=o73d2bA0Q1qyv2dHc8YTTVnFiWUKJP6wo3soKs2CMs51g1mw6mT9KWp3CubbmXqKV 7jDJnkWgW2eHCIecUVldJLpSpOitXyyIfVzVLaylvo8gfuhgJQn9mRNig6hNX/QyG+ /QZwbTuYFYIrv7KTbuBzYlYELHqpuq2TL9ggRByBMyd7lUC0hHXCt+hLSitYEO7U+3 t2wQtTbNsYB4HF7njtrzdZ4H7NVR+2ycXxVIhA4lpztLi/09CnEV0JGSQjyEWcnF1r hbyljf7qNB4lCkSM0Md5qcGm3GA3yI5bNLTjAF8PHDxJeVa+obGmk5Awlekh8lvKTN iCvk4DfUpQ8Xg== Date: Mon, 23 Mar 2026 17:02:44 +0000 From: "Lorenzo Stoakes (Oracle)" To: Suren Baghdasaryan 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 Subject: Re: [PATCH 1/1] mm/vmscan: prevent MGLRU reclaim from pinning address space Message-ID: References: <20260322070843.941997-1-surenb@google.com> <65cb38ee-2815-4b11-929d-3fc1528cc620@lucifer.local> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Queue-Id: B2611C000E X-Stat-Signature: xn15cdai8awo8hm7ro4mba41ytqohfut X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1774285370-746071 X-HE-Meta: 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 yqkzdzWf QBHYS0mgoe7Gvm2FUCJmdIsOsZwezEWlBfRSfe8nSjRNrheEt4eFB+s5Mk/6whvxcl2vM9PCiAEg3Q6GwULfxdJhzMPpRW1QwgGXj9UiZtvZspY7mosekwrArl3A0TzyJHici/4XT/Vult3E6Q+irQ9KGwohPdrGiumml1LyoROFS5S4nZYd9lZV67XkIYoCDSSzM7STDmTNPxl9+LsMMQxJ4lvkfz7UQya7e/zn09atHNRDEOkuPO6wddnQ3U18brIYlO+M6W4Dqw0pMGJpy1YsVlcoX2TLMdPpb 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 09:26:02AM -0700, Suren Baghdasaryan wrote: > On Mon, Mar 23, 2026 at 6:43 AM 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 and > > > 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 due > > > 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, Lorenzo Cheers, Lorenzo