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b=Jb+hZ8T4MSfmF5G0y14DPiO3Mhq5J0qHUrmIpKQbmcGMq4FjOe938Bujj+xZ5FEy2 EQCBhZKqHMXlzPSyThaN/WFVEmS9GpHpKoTp4B4kxMO7DBGiK3ON7na2nBqmftPDy2 IyK5FKc61XX+ubMOqBn3fygMsUxnd32hH4t+NTKk= Date: Sat, 30 Nov 2024 18:40:17 -0800 From: Andrew Morton To: Seiji Nishikawa Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, mgorman@techsingularity.net Subject: Re: [PATCH] mm: vmscan: account for free pages to prevent infinite Loop in throttle_direct_reclaim() Message-Id: <20241130184017.7290e756a5f2199b463a7172@linux-foundation.org> In-Reply-To: <20241130161236.433747-2-snishika@redhat.com> References: <20241129043936.316481-1-snishika@redhat.com> <20241130161236.433747-1-snishika@redhat.com> <20241130161236.433747-2-snishika@redhat.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 8360540002 X-Stat-Signature: 9ght4g3na3wusnmeinxzmmbrgupf8ujz X-HE-Tag: 1733020809-348261 X-HE-Meta: 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 WsSOLRJq hS2n6hjxmIp+fEUjncAJB+rOs3wOTMkpdlLGcWOW56eabTXfITuULb6Xat5VXKYpOQyQ0JdRJV4nxnFen5GqOm6znhnItGO6TqwbCXzoYmNFRAIDz/tUZt221eRz0JBJUflLDXueVvFJc8h9kKBx/DYKpTXFKGUQ4UzVbDGcnaUvRGrv0PNB94IyeZe3YqOKANpGNMGPrbARhjBUL2f06NkeNPN7LTLZDylUWdtFj/f4k15KBmE16crnu0p0ehoGGc9dyLgV2h7nXrc8gyKNodca4SNnrhTANFw2ZeBfTQAYPqKOXDKIgqkVbkezPDwOLHiev 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: List-Subscribe: List-Unsubscribe: On Sun, 1 Dec 2024 01:12:34 +0900 Seiji Nishikawa wrote: > The kernel hangs due to a task stuck in throttle_direct_reclaim(), > caused by a node being incorrectly deemed balanced despite pressure in > certain zones, such as ZONE_NORMAL. This issue arises from > zone_reclaimable_pages() returning 0 for zones without reclaimable file- > backed or anonymous pages, causing zones like ZONE_DMA32 with sufficient > free pages to be skipped. > > The lack of swap or reclaimable pages results in ZONE_DMA32 being > ignored during reclaim, masking pressure in other zones. Consequently, > pgdat->kswapd_failures remains 0 in balance_pgdat(), preventing fallback > mechanisms in allow_direct_reclaim() from being triggered, leading to an > infinite loop in throttle_direct_reclaim(). > > This patch modifies zone_reclaimable_pages() to account for free pages > (NR_FREE_PAGES) when no other reclaimable pages exist. This ensures > zones with sufficient free pages are not skipped, enabling proper > balancing and reclaim behavior. We'll want to backport a fix for this into -stable kernels. For that it's best to be able to identify a suitable Fixes: target, to tell others whether their kernel needs the fix. Are you able to help identify that commit? Thanks. > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -374,7 +374,14 @@ unsigned long zone_reclaimable_pages(struct zone *zone) > if (can_reclaim_anon_pages(NULL, zone_to_nid(zone), NULL)) > nr += zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_ANON) + > zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_ANON); > - > + /* > + * If there are no reclaimable file-backed or anonymous pages, > + * ensure zones with sufficient free pages are not skipped. > + * This prevents zones like DMA32 from being ignored in reclaim > + * scenarios where they can still help alleviate memory pressure. > + */ > + if (nr == 0) > + nr = zone_page_state_snapshot(zone, NR_FREE_PAGES); > return nr; > } > > -- > 2.47.0