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 iih75J1R yadRRmQPK54gph6LMajxh0OODd6wauyiNCWU6y3Iq1jKJvBl7elVMWO3n7gyGKMkX0X8UH0xPzUfQVJt6zumRCiBheEFEPrmHPosEid6aNL9h22icP5706qd2TrEYTkKOpYszJPOWxYuHakGA5RESvDxB6Z1Czx8XILc+dfmZ7q9qAMYOnewHkhnzQ9oVxTOZjDlEl+FjAjw2euY8DI1YEddd7KBj9kcxyaSblBpeVCkJQfoWHQGgAk8DCLifsgBMXIFyFI3j6AOM+j9r0ZyvFzxqTdAhaSofvu22Y+9EpiYVX6eu4+F8ziAD42XYq9NRFbWrAjIevNXclNWojVrxL2FtasdqGfr5EY1KKaVzOb/uOO9jMjAiohEvqxTlYtmHLR0WhgyJPyaYJmdKx2uCq24uqsWYrRKwT6PWCsWRGeM4T1w= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon Sep 28, 2026 at 6:06 AM EDT, Kiryl Shutsemau wrote: > From: "Kiryl Shutsemau (Meta)" > > Tests scattered through the collapse path decide what a collapse is > allowed to do by asking whether khugepaged started it. Between them they > settle: > > - which VMAs are eligible, and how hard to try for a folio; > - how many empty, swapped-out or shared PTEs a window may contain, and > whether a sub-PMD window is held to a stricter rule than a PMD; > - whether a range has to look used, and whether a MADV_FREE'd page is > left alone; > - whether the PMD is mapped as part of the request, and whether dirty > pages are worth writing back and retrying. > > None of those is a fact about khugepaged. Each is something the caller > decided before asking, and the collapse code should not have to look up > who called to find out. > > Add struct collapse_policy for the caller to fill: khugepaged from its > own settings, MADV_COLLAPSE from the fact that a user asked explicitly. > Every test becomes a read of a field, and cc->is_khugepaged goes, having > no reader left. > > The PTE limits come as two sets, one for a PMD-sized window and one for > anything smaller, so that the helpers pick a set for the order and read > it. khugepaged takes no swapped-out or shared PTE into a sub-PMD window, > and empty PTEs only when the knob says all or nothing; the warning for a > knob value in between moves to where khugepaged fills its policy. The > fields only one side reads say which: anon_ or file_. David Hildenbrand > asked for both. > > khugepaged fills the policy once per scan pass, MADV_COLLAPSE once per > call. That is the one change in behaviour. The max_ptes_* limits and th= e > defrag setting behind the allocation mask are sampled once per pass rathe= r > than on every table. A table scanned early in a pass and one scanned lat= e > are then treated alike. > > collapse_file() also drops a NULL check on the collapse_control. It has > one call site, reached only from collapse_single_pmd(), which dereference= s > cc unconditionally, so the check was already dead. > > Assisted-by: LLM > Signed-off-by: Kiryl Shutsemau (Meta) > --- > mm/collapse.h | 41 +++++++++++++- > mm/khugepaged.c | 147 +++++++++++++++++++++++++----------------------- > 2 files changed, 118 insertions(+), 70 deletions(-) > LGTM. Reviewed-by: Zi Yan --=20 Best Regards, Yan, Zi