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Tue, 04 Aug 2026 13:47:56 -0700 (PDT) Date: Tue, 4 Aug 2026 16:47:52 -0400 From: Johannes Weiner To: Zi Yan Cc: "Lorenzo Stoakes (ARM)" , Andrew Morton , Matthew Wilcox , William Kucharski , David Hildenbrand , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v2 1/2] mm/huge_memory: use folio's memcg inside __folio_split() Message-ID: References: <20260730-add-gfp_account-to-xas_split_alloc-v2-0-5a56c2361d85@nvidia.com> <20260730-add-gfp_account-to-xas_split_alloc-v2-1-5a56c2361d85@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 3013E100006 X-Rspam-User: X-Stat-Signature: k73e3ucrgb6u6s13eiz3cohr9c73esoe X-HE-Tag: 1785876480-338418 X-HE-Meta: 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 m7ghiTIJ lc30LQAsey3MN4nPExyHPaQNoG0/CAhwy6XjcFVQxZnzqX1jIZniZHCO7rahUgT1TGEBJyed5feJXpHk21OrhonJ99ZAuav0UmuDS7Myaaza/VpKfopfuR5PBE/sh5+uZzBiuD+E49tnD/+XUEb5Yo8p1cw4/cKrNxEGRlfuV64UU+ohykzRisBuwmzAJLFLiey00o92Ed1GGahyNnuG6jcoTzLksYjIApX6+poeaPePQCldr1HKJWSN6QwiGukb9gfrW0FKULZ6bYkc5jM8QyIcjToV7qTjunhNbEcDv6GO3qWMTqHeYaW0UXyscfPAhPuXALhPfGsWRqKMn/KjLgOOdYGqeNEns0a6cftD8fVjAibC57Tbb8wrf/1cCJB8RhFEWUDp0ui449XvB6GR1UUP5E4enTaxLVlYCUmQdII/MZs1IvHImr+LFDOHSVKFPMgpMtP67QBnaNtWkKmAAoVawA9u7Is5I3w1K Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Aug 03, 2026 at 11:02:30AM -0400, Zi Yan wrote: > On Sat Aug 1, 2026 at 5:36 AM EDT, Lorenzo Stoakes (ARM) wrote: > > On Thu, Jul 30, 2026 at 10:18:00PM -0400, Zi Yan wrote: > >> During a pagecache folio split, an xarray node allocation can happen and > >> needs to charge at folio's memcg instead of folio split invoker's memcg, > >> because for example folio split can happen during reclaim and reclaim's > >> active memcg might not be folio's memcg. Switch to folio's memcg at the > >> beginning and switch back afterwards. > > > > I assume this is the only allocation? I guess in general it makes sense to have > > the folio's memcg be active here regardless. > > > >> > >> Suggested-by: Johannes Weiner > >> Fixes: 6b24ca4a1a8d4 ("mm: Use multi-index entries in the page cache") > > > > Cc: stable? > > Like you said above, only xas_split_alloc() is affected. And we have not > seen related workingset regression report (like what Johannes reported > in commit 7b785645e8f13 ("mm: fix page cache convergence regression")). > It might be OK to not backport. > > Johannes, what is your take on this? Yeah, let's Cc stable. It would be a bear to debug if you ran into this at scale. Which I think you could with certain workloads. The patches are straight-forward enough. It favors a backport.