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Howlett" , David Hildenbrand , Vlastimil Babka , Jann Horn , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Mike Kaplinskiy , zhaozhengzhuo Subject: Re: [PATCH] mm/madvise: swap in CoW'd MAP_PRIVATE-file mappings on MADV_WILLNEED Message-ID: References: <20260904-madv-will-need-map-private-v1-1-6b83cc99fcff@kernel.org> <20260905171757.ba8b0f8f0f18ebd04418bfeb@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260905171757.ba8b0f8f0f18ebd04418bfeb@linux-foundation.org> X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 08C85A0002 X-Stat-Signature: dp1nofzrwjo5cksny8pp1m7zsybxyfs6 X-Rspam-User: X-HE-Tag: 1788784380-87272 X-HE-Meta: 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 DMGImHNf kkXJBa7TwVR9HwzlnYIOiON2A6vyc+GN+0YkymsejkB9V/7RV5C1MRKakfXrC4kas16qZZ6ydf2l3bJ4xF2K8t80Kp0e6RONz17kMxOxBnGMxD8Q8rRatMQ54CKJGS9pdm8fcRvfTSj1lS16//J84RFOX5GKwCgO/CY5YbrXpL1erhXpI0kTMmwQ/ZSgefZDeQuJq/p2MCOc9z/g/rfqsPCz1zJkcc7o22A3VdUWYCSQrt1Ju4ggSEbLPlzZe4MPwvfLCWuMFyRKdNRexrXfzohJdTk+Ob5Z8j6mPlYeyG9g7B5AZkk/x798CPGu5LnDR6QLY+D8nMgPcAhM7DFXIK80wHQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, Sep 05, 2026 at 05:17:57PM -0700, Andrew Morton wrote: > On Fri, 4 Sep 2026 17:01:37 +0100 "Lorenzo Stoakes (ARM)" wrote: > > > Andrew - could you swap the patch out in-place with below? Thanks! > > > > np. > > > Currently MADV_WILLNEED treats file-backed and pure anonymous mappings > > entirely separately - using POSIX_FADV_WILLNEED (equivalent of a readahead) > > for the former and a tree walk and swap in to swap cache for the latter. > > > > MAP_PRIVATE-file backed mappings straddle the two and currently get treated > > as if they were purely file-backed, meaning any swapped out private pages > > remain swapped out. > > > > Resolve the issue by explicitly checking for CoW'd MAP_PRIVATE-file backed > > mappings and performing both walks in this case. > > > > Since the logic checks for vma->anon_vma this means un-CoW'd > > MAP_PRIVATE-file backed mappings retain only the single file walk. > > > > Reported-by: Mike Kaplinskiy > > Closes: https://lore.kernel.org/all/CABeknB_S2XJSHFgnHdgnN0rjzHhH4oQJs_APq9fvxHztQ_pgiA@mail.gmail.com/ > > Signed-off-by: Lorenzo Stoakes (ARM) > > The failure mode looks pretty obscure, so I'm thinking that no backport > is needed. Well it's not even really a failure mode so much as a 'known limitation' :) So yeah agreed. -- Cheers, Lorenzo