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Howlett" , David Hildenbrand , Vlastimil Babka , Jann Horn , Pedro Falcato , Muchun Song , Oscar Salvador , linux-mm@kvack.org Subject: Re: [PATCH 3/6] mm/mremap: reaccount on unmap failure only if accounted Message-ID: References: <20261030-b4-mremap-pre-split-v1-0-c1829811aed0@toxicpanda.com> <20261030-b4-mremap-pre-split-v1-3-c1829811aed0@toxicpanda.com> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261030-b4-mremap-pre-split-v1-3-c1829811aed0@toxicpanda.com> X-Rspamd-Queue-Id: 397DEA0006 X-Stat-Signature: iyhttrcoatn9sy7cnyxu9xb67zgja5j3 X-Rspamd-Server: rspam04 X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1793625468-233614 X-HE-Meta: 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 ZoLST4P8 qi3elmSmSYIvjk+6mJ9416ZqtA4iTrs55f8a47Dcw6EojTB8vvaDb1mEHnuTFZRyCPF2/tqBwJ+NH/7jjD6sTsINWRTdL6Rx+dvyBv3pMzQkfhuwAwrJ1bmRavl+Z6mHcSvZVyKvw21HXZhYvia6WENkTKUMukUtLv3ueHKphRjN+e7Zbq6MjnR/5XFI19D2w36b2eVA8f0vkpHXxb9R1sA/Dk01VgqTOcpaR/g41+V4KVVDeAaCXgfMfAT1GvQ4jFIdQtE5UEvdhSnldXMxFk9XsyG7EHS3vfmlU6AOfU8bKYudMuU3FaOenuUz9S+Ivd3xrQR3R09YZy5WB1DE+bhWa7Q== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Fri, Oct 30, 2026 at 02:42:48PM +0000, Josef Bacik wrote: > When the unmap of the source range fails at the end of an mremap() move, > the length of the range is charged to vm_committed_as even if the VMA was > never accounted, for example a MAP_SHARED or MAP_NORESERVE mapping. Nothing > ever uncharges these pages, so each such failure permanently inflates the > committed memory count. > > This was reproduced with fault injection: each failure on a shmem mapping > left Committed_AS higher by the size of the moved range after everything > was unmapped. I'm guessing this wasn't noticed because it's nigh on impossible to hit these in reality and if you do the process is doomed anyway. > > Fix by charging the range again only when accountable_move is set. > > Fixes: b714ccb02a76 ("mm/mremap: complete refactor of move_vma()") Ugh, I definitely made some mistakes on that one :) I think this doesn't really need stable in practice as the only way you hit this in practice is extreme memory pressure + a fatal signal. And then the process is going away anyway... > Signed-off-by: Josef Bacik LGTM so: Reviewed-by: Lorenzo Stoakes (ARM) > --- > mm/mremap.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/mremap.c b/mm/mremap.c > index cf746bafdee4..6f941aeb1b5f 100644 > --- a/mm/mremap.c > +++ b/mm/mremap.c > @@ -1247,7 +1247,8 @@ static void unmap_source_vma(struct vma_remap_struct *vrm) > vrm->vmi_needs_invalidate = true; > if (err) { > /* OOM: unable to split vma, just get accounts right */ > - vm_acct_memory(len >> PAGE_SHIFT); > + if (accountable_move) > + vm_acct_memory(len >> PAGE_SHIFT); > return; > } > > > -- > 2.55.0 > -- Cheers, Lorenzo