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RGEs9BzLlkdrH8yw1DgNJI5jdH5SaeoBoNmTJNF2KtZ0VFbTqt36C84Tk7Uu5PIeeNT0EukxSUA/oc2rq1laQQF/7GkVvh0r8adD/RIwHFTQ7/umZGOWWPXrRbLh/DwEvz8AnmrAdAKcmLJynV3cxbJLdE5IOQAc/mrji8fJUyu0eoKQPl10rXGzqAF4BfyZUu4zkjuntIPqStmlVuG7CNtXyKlv5QdWj3W7xmevvRrTem5J4aAvFKxDlpyazIMPW0Z+dfHMTXQvfXs3RD/v10coN3cHSNutiEd/W8V4k414iHgxdi9z66ST/7uE/Gogdo2yitVKvFMqQlb4C3PzFYsLfgUy+WG/6CXFu1rY/c4R/tI9JjelJlkdyESN9Bp2lBFy36G5b19Qw50PTGDPPEtX4h3XBqLejKKZEXFbGH4o6nzM= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu Sep 10, 2026 at 8:02 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. > > 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 judged 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 | 31 ++++++++++++- > mm/khugepaged.c | 114 ++++++++++++++++++++++++++---------------------- > 2 files changed, 93 insertions(+), 52 deletions(-) > Great cleanup! Thanks. Reviewed-by: Zi Yan --=20 Best Regards, Yan, Zi