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charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: srcn8cp1rbtdpxsoxb7coocp44n4qddt X-Rspamd-Queue-Id: B89FC100006 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1719531565-500029 X-HE-Meta: U2FsdGVkX1/xyPGhL04lJ3W4godHt5ZM1BuXg6PwE+XQC1OkQ1gDWp4LipIa9Jl1jrRrD+u5RtAlDOWsk4PG9aJVyMGgXrFs00FabgJhtLCJazNvpBPW09Qi/ThmBSFH59u8NuvDD5WH5EKG8Ifif1+s3KPGDPk3R6gh1vW/40S1vbLUIV4jr6N7v8FU6pXWQMdRNvXqxX8u+E05EUibqJOZMu2tOPRap/NNoieYcVyPPKUM0TVVlo9wvCmVmot0w8caUrhqR8cQ57YO+Yjas2xqiXMHY4SZUjlmANx1tLqcAIR70T+agh/hegl5ndvsZNY9TMKkbFuRj7u30rwA8t/QwYGqwqivn58HIFOpwR5Chtztd6vAINQNQppto2YcyMlFXfd0TSvbywGth1ly+5wbVXCeI2DMqJZqEnMwRzivrBdO/IQTQpZksi0PoVQm09go5W2UvN4Qa0WjpohvNr8kSgH3TGZckXh9+eIcBWLxcyqBi2Z5MmEXyVb0MGT0XA5BU9EK1mMR5Tf8v8pxqvSBXsM4SsKNemaAQyU9Bwz9jpoav2LA9RkkhBlVzRP09RfNF9QAj/naCK/YeavA0JCX0VtThIPJZulYyWT4qbmm067AIfe5myzIdsDAwMfzERnpKjPHaF+UrhpiINBSPQNV1+D+MMN3sJEjz4sK4tXcgJG+rtPGApMgRY9F21klNoCHrEdzAtt4fa5O1p9GiORx3zjgaw5ux8mfTAQ+hqVwiJuvyrnemsVsqzDLrRX729U+LJaseFOwkEmN1wa2RZRGiRIYtLH+O1DYKw0DCknFvORFZaLOa2fbnNSkeIG3Ow8xiIE+mftcVkAr3i+0jJROeEVwNw1n9QkbJyC3Aorqlm1WeQKXCG1oW6/MPsCbsdiRHxR6rqsbT9LjG4jcCWd1s8igI2VGmkupvTFf/5uoWmkEJ6tiRU2M99W8qrfTlykW70g65OIMUK/hFfw pjOLduNH F1G/pnnBUsTeFY0IdJhpN9si+0BYd9tkud3sudexE0ECCdA8U1ozIuWjDbyVid3/NpGYrD7v9ojU/Ze0BgUh8PkJypdkG6AGYWSxzxzcWjntekrFhauFZfUHfeqFBLWiUoal4/+4ufRz/IJ//s5MxO9f68eJMTSyWgf8oB1nzQNajzQl+1kEge19pizEsUlTaT9G+dFc4o6QiEeLE1UdDdQNj7koBeyxhisiufS6RoMxKe7T4F8pHuH61llF5wfJ0VOA36k2B25obYn/PxwpsrdznaOuPgeKDqSqps3kAP8A43iMLfYMRL3OgXuXMuP5pZ/6AnyYUsZDdJthdr9oz5ZGGr0RRk774PZnTYvPfCUQrMm5HCxc8OqS/A7CdkgkAl1fpBFVNe+J+aJE0Ow12GewHgyD96WhE+yPOCVnRiJ/BY1k= X-Bogosity: Ham, tests=bogofilter, spamicity=0.069113, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Jun 27, 2024 at 4:32=E2=80=AFPM Andrew Morton wrote: > > On Thu, 27 Jun 2024 19:19:40 -0400 Peter Xu wrote: > > > Yang, > > > > On Thu, Jun 27, 2024 at 03:14:13PM -0700, Yang Shi wrote: > > > The try_grab_folio() is supposed to be used in fast path and it eleva= tes > > > folio refcount by using add ref unless zero. We are guaranteed to ha= ve > > > at least one stable reference in slow path, so the simple atomic add > > > could be used. The performance difference should be trivial, but the > > > misuse may be confusing and misleading. > > > > This first paragraph is IMHO misleading itself.. > > > > I think we should mention upfront the important bit, on the user impact= . > > > > Here IMO the user impact should be: Linux may fail longterm pin in some > > releavnt paths when applied over CMA reserved blocks. And if to extend= a > > bit, that include not only slow-gup but also the new memfd pinning, bec= ause > > both of them used try_grab_folio() which used to be only for fast-gup. > > It's still unclear how users will be affected. What do the *users* > see? If it's a slight slowdown, do we need to backport this at all? I think Peter meant the warning reported by yangge? Peter also mentioned the patch subject is misleading. I agree. So how's about "mm: gup: stop abusing try_grab_folio()"? > > > > > The patch itself looks mostly ok to me. > > > > There's still some "cleanup" part mangled together, e.g., the real meat > > should be avoiding the folio_is_longterm_pinnable() check in relevant > > paths. The rest (e.g. switch slow-gup / memfd pin to use folio_ref_add= () > > not try_get_folio(), and renames) could be good cleanups. > > > > So a smaller fix might be doable, but again I don't have a strong opini= on > > here. > > The smaller the better for backporting, of course. I view the fix to the warning as just by-product of the clean up. The whole patch is naturally integral IMHO. We can generate a smaller fix if it is too hard to backport. However, it should be ok since we just need to backport to 6.6+. >