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Sat, 22 Mar 2025 18:34:09 -0700 (PDT) Date: Sat, 22 Mar 2025 21:34:05 -0400 From: Johannes Weiner To: Brendan Jackman Cc: Andrew Morton , Vlastimil Babka , Mel Gorman , Zi Yan , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 3/5] mm: page_alloc: defrag_mode Message-ID: <20250323013405.GC1894930@cmpxchg.org> References: <20250313210647.1314586-1-hannes@cmpxchg.org> <20250313210647.1314586-4-hannes@cmpxchg.org> <20250323005823.GB1894930@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250323005823.GB1894930@cmpxchg.org> X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: EBB9B180004 X-Stat-Signature: harmep9sbrcnykgundtc48nh4pq6wpj3 X-Rspam-User: X-HE-Tag: 1742693650-23001 X-HE-Meta: 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 m3BvuomP 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000002, 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 Sat, Mar 22, 2025 at 08:58:27PM -0400, Johannes Weiner wrote: > On Sat, Mar 22, 2025 at 04:05:52PM +0100, Brendan Jackman wrote: > > On Thu Mar 13, 2025 at 10:05 PM CET, Johannes Weiner wrote: > > > + /* Reclaim/compaction failed to prevent the fallback */ > > > + if (defrag_mode) { > > > + alloc_flags &= ALLOC_NOFRAGMENT; > > > + goto retry; > > > + } > > > > I can't see where ALLOC_NOFRAGMENT gets cleared, is it supposed to be > > here (i.e. should this be ~ALLOC_NOFRAGMENT)? Please ignore my previous email, this is actually a much more severe issue than I thought at first. The screwed up clearing is bad, but this will also not check the flag before retrying, which means the thread will retry reclaim/compaction and never reach OOM. This code has weeks of load testing, with workloads fine-tuned to *avoid* OOM. A blatant OOM test shows this problem immediately. A simple fix, but I'll put it through the wringer before sending it.