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Howlett" , David Hildenbrand , 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> <55ce7bee-c0e0-4051-8bc4-26cf3aa3f7e9@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55ce7bee-c0e0-4051-8bc4-26cf3aa3f7e9@kernel.org> X-Stat-Signature: rubf955yuyjhymayr7yijiazdikrqrhz X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 6B4F1140008 X-Rspam-User: X-HE-Tag: 1788794867-204065 X-HE-Meta: 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 2sR2Sl96 EGi3LI0DnQmVX75R123hvvzRwI40oXykirIe5EL4CcapLl1uTdcwtXO7TYKZE6WMLlH9EpFbdnCm0v1W4K8WaKJtO8/0dbyh7C26ukuuQlB8sesBS8OA7zMcaCvfLAl+PPoa3jijuZdl5iafViSBFXPWIKabfvCox5J5sb219mfMRs38viHNCKM7fsY6KAZM2kHpI/8dsFiUrDpAg1RZCf4xyJvh1fdc/4jcRTlzqjbySTj6mRYws1O6cjSOFdzvCoxb5yDgAu4nOUmiFklMAscTolTxKg47/kbuxsJfJug+Iu30GiTHtq+eISwNX2PtP/sabZOZkUNwek4beanjctTpCdg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Sep 07, 2026 at 05:09:34PM +0200, Vlastimil Babka (SUSE) wrote: > On 9/7/26 14:32, Lorenzo Stoakes (ARM) wrote: > > 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. > > Yeah, as we know madvise() just an advice after all, the kernel is free to > ignore it :) > > (MADV_DONTNEED and friends enter the chat) Haha yeah, another brilliant footgun invented by the proud folks at kernel mm, catch us next time with some prctl's and BPF APIs! ;) > > > -- > > Cheers, Lorenzo > -- Cheers, Lorenzo