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dkim=pass header.d=oracle.com header.s=corp-2021-07-09 header.b=0BpFUI8v; dkim=pass header.d=oracle.com header.s=corp-2020-01-29 header.b=Q8cqkR1h; dkim=pass header.d=oracle.onmicrosoft.com header.s=selector2-oracle-onmicrosoft-com header.b=osf1apv0; dmarc=pass (policy=none) header.from=oracle.com; spf=none (imf20.hostedemail.com: domain of chuck.lever@oracle.com has no SPF policy when checking 205.220.165.32) smtp.mailfrom=chuck.lever@oracle.com X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 7C18CD0000A9 X-Stat-Signature: g5r6u5twukfucspoyqsrosonnixd34du X-HE-Tag: 1631026448-735305 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: > On Sep 6, 2021, at 8:41 PM, NeilBrown wrote: >=20 > When does a single-page GFP_KERNEL allocation fail? Ever? >=20 > I know that if I add __GFP_NOFAIL then it won't fail and that is > preferred to looping. > I know that if I add __GFP_RETRY_MAILFAIL (or others) then it might > fail. > But that is the semantics for a plain GFP_KERNEL ?? >=20 > I recall a suggestion one that it would only fail if the process was > being killed by the oom killer. That seems reasonable and would suggest > that retrying is really bad. Is that true? >=20 > For svc_alloc_args(), it might be better to fail and have the calling > server thread exit. This would need to be combined with dynamic > thread-count management so that when a request arrived, a new thread > might be started. I don't immediately see a benefit to killing server threads during periods of memory exhaustion, but sometimes I lack imagination. > So maybe we really don't want reclaim_progress_wait(), and all current > callers of congestion_wait() which are just waiting for allocation to > succeed should be either change to use __GFP_NOFAIL, or to handle > failure. I had completely forgotten about GFP_NOFAIL. That seems like the preferred answer, as it avoids an arbitrary time-based wait for a memory resource. (And maybe svc_rqst_alloc() should also get the NOFAIL treatment?). The question in my mind is how the new alloc_pages_bulk() will behave when passed NOFAIL. I would expect that NOFAIL would simply guarantee that at least one page is allocated on every call. -- Chuck Lever