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b=fIXuH3oPbKOQqHa+sb82A1lqdGEE0KcOgjF+PatDaFm43q0tXh6aZfgHVTPVkzhK8 jR0yOowvlHMK1RAA3Gh8EHvmNFZ190IgWKCan6bh89OQ1KHejC1cxKJrwPjErgz80o GtZ2nO9DmLB3ry90DZ0LhmjrKBrm9bdOrPRHbKa5tH3YviCk87S5bMVhZiS13bbaTE diYUiyFFeavhUjIW73ix4dDOFSqJsVIrEM0rBfDWS9QMA8oCUgO6HMKrQk71Ol0HKC t7wrO2vnOAMFY65gPgYkcD9GNDNEe1748kh2kCS7PeaNEk3VFGgZjLQKCOwc3IihDq 15/bp4/cVuzDg== Message-ID: <68fd8182-cdfb-4f11-95de-1472e6c92d33@kernel.org> Date: Thu, 29 Oct 2026 14:37:03 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 1/8] mm/page_alloc: reset can_retry_reserves when the slowpath restarts Content-Language: en-US To: "Gregory Price (Meta)" , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, muchun.song@linux.dev, osalvador@suse.de, david@kernel.org, akpm@linux-foundation.org, ziy@nvidia.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, ying.huang@linux.alibaba.com, ljs@kernel.org, liam@infradead.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, brendan.jackman@linux.dev, hannes@cmpxchg.org, mgorman@techsingularity.net, anshuman.khandual@arm.com, stable@vger.kernel.org References: <20261028211930.3504634-1-gourry@gourry.net> <20261028211930.3504634-2-gourry@gourry.net> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 9A460160006 X-Stat-Signature: q6fd96cyx4zwzub66486ipw67d5imip6 X-Spam-Status: No, score=-17.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1793281031-861222 X-HE-Meta: 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 PPF/1ByQ Ic9a7jmjEn+cHQ2EcGlPoHPJXNFSjb+Ey6K6aFj7tc5m5132sTYKEkGbaCiI5OS4Rh34940kskc9b4fIMNrkanMyXw3yqWBYpT5A+1R7KHa3kOSQY2G18IXV3eNVdtQFutxG6jWr1mPsWG+d+UC20ZuH5JY98YQAXXmBHZmvGuL7UyVLwggviOpU42ESI5IqBn74pGqrsFl1zESwjPAJapd43MdI4+8kEtsIClYsdvkFg+LYELKFu9H/NEqRJj5kvVQsazexEaMLZ1e1WNgqsbvmaOwQN2WavhNE2TQm3GZF5AbnujjAE/vLkXlexcxZencPEmDYl3XPFUPgPlK/tDW3Fdr1un6XbpZWEGURcqE5RqGQ/VZWxLGQ1p4zId2CoRfRu5YV/uBHk+1SaQMutKA5Zf815TpS08+uQtQktA5jMaTbLvVrVEHEUz/BPvSaRdzEOfKIF8bsPUbDkLtUFJcrwtw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 10/28/26 22:19, Gregory Price (Meta) wrote: > Commit 2c4c3e29897d ("mm/page_alloc: simplify __alloc_pages_slowpath() > flow") retries an allocation once with reserve_flags when the caller > becomes eligible for reserves, guarded by can_retry_reserves. The flag > is set at its declaration and never reset. > > A restart after a cpuset update or a zonelist rebuild drops > reserve_flags I don't follow, nothing "drops reserve_flags"? after the restart, there will still be a get_page_from_freelist() without them followed by get_page_from_freelist() with them, right? > and comes back with can_retry_reserves already false, so a > caller that cannot reclaim, such as GFP_NOWAIT | __GFP_MEMALLOC, fails > without trying the reserves again. The "goto retry" triggered by can_retry_reserves actually drops nodemask and recalculates preferred zones. Perhaps "can_retry_reserves" wasn't the best name. > Reset can_retry_reserves at restart. Only a cpuset or zonelist change > restarts the slowpath, so the retry still runs at most once per change. > > With kprobes failing every attempt without reserves and the first with > them, and a memory block onlined during the walk, the allocation > returned NULL in 3 of 3 runs, and a page in 3 of 3 with this change. So IIUC the allocation was racing with a memory online in a way that it would fail if the online happened fully after the allocation. So this just turns part of the race window into the allocation's favor? > Fixes: 2c4c3e29897d ("mm/page_alloc: simplify __alloc_pages_slowpath() flow") > Cc: stable@vger.kernel.org > Signed-off-by: Gregory Price (Meta) I mean it's not wrong and if patch 5 depends on it (unless it also only fixes a racy window in the same way I think is happening here) then so be it. But the commit log would need correcting. > --- > mm/page_alloc.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 2daf358269ae..78569ac6f2d9 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -4783,7 +4783,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > unsigned int zonelist_iter_cookie; > int reserve_flags; > bool compact_first = false; > - bool can_retry_reserves = true; > + bool can_retry_reserves; > unsigned long alloc_start_time = jiffies; > > /* > @@ -4817,6 +4817,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > no_progress_loops = 0; > compact_result = COMPACT_SKIPPED; > compact_priority = DEF_COMPACT_PRIORITY; > + can_retry_reserves = true; > cpuset_mems_cookie = read_mems_allowed_begin(); > zonelist_iter_cookie = zonelist_iter_begin(); >