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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: D6664180003 X-Stat-Signature: 7e5bxzxf9pf7ohy11xidc5zox1go4oxe X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1742734151-57982 X-HE-Meta: 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 zNTPwJrn 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.006710, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: >> >> c) In -next, there is now be the option to use folio lock + >> folio_maybe_mapped_shared() == false. But it doesn't tell you into how many >> VMAs a large folio is mapped into. >> >> In the following case: >> >> [ folio ] >> [ VMA#1 ] [ VMA#2 ] >> >> c) would not tell you if you are fine modifying the folio when moving VMA#2. > > Right, I feel like prior checks made should assert this is not the case, > however? But mapcount check should be a last ditch assurance? Something nice might be hiding in c) that might be able to handle a single folio being covered by multiple vmas. I was thinking about the following: [ folio0 ] [ VMA#0 ] Then we do a partial (old-school) mremap() [ folio0 ] [ folio0 ] [ VMA#1 ] [ VMA#2 ] To then extend VMA#1 and fault in pages [ folio0 ][ folio1 ] [ folio0 ] [ VMA#1 ] [ VMA#2 ] If that is possible (did not try!, maybe something prevents us from extending VMA#1) mremap(MREMAP_RELOCATE_ANON) of VMA#1 / VMA#2 cannot work. We'd have to detect that scenario (partial mremap). You might be doing that with the anon-vma magic, something different might be: Assume we flag large folios if they were partially mremapped in any process. Then (with folio lock only) 1) folio_maybe_mapped_shared() == false: mapped into single process 2) folio_maybe_partially_mremaped() == false: not scattered in virtual address space It would be sufficient to check if the folio fully falls into the memap() range to decide if we can adjust the folio index etc. We *might* be able to use that in the COW-reuse path for large folios to perform a folio_move_anon_rmap(), which we currently only perform for small folios / PMD-mapped folios (single mapping). Not sure yet if actually multiple VMAs are involved. Just throwing it out there ... > > (actually at least one of the 'prior checks' for large folios are added in a > later commit but still :P) Yeah, I'm looking at the bigger picture; small folios are easy :P -- Cheers, David / dhildenb