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From: Shakeel Butt To: Boris Burkov Cc: Klara Modin , akpm@linux-foundation.org, linux-btrfs@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, kernel-team@fb.com, wqu@suse.com, willy@infradead.org, mhocko@kernel.org, muchun.song@linux.dev, roman.gushchin@linux.dev, hannes@cmpxchg.org Subject: Re: [PATCH v3 1/4] mm/filemap: add AS_UNCHARGED Message-ID: References: <43fed53d45910cd4fa7a71d2e92913e53eb28774.1755562487.git.boris@bur.io> <20250820225222.GA4100662@zen.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250820225222.GA4100662@zen.localdomain> X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: 353F520008 X-Rspam-User: X-Stat-Signature: 647fsepj8gdt3y44hkpcm3p4us8eaiga X-Rspamd-Server: rspam09 X-HE-Tag: 1755733995-190288 X-HE-Meta: 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 7DYYDBgf d8rK9yJf5wPSk0FVAjUNH+12yeQMje3n/DpyBYI1boBE9nXcNCNZ9drzDVh2ocsekpRLsTQSAslG6v55gRVWpeNd4csbBpAw6XI8VzOrQ1TiSxxpgdNiZggj0LZ0I4dGHc0aJbVAXDyUpulP9us4in9BXWd/vnn+PFxQwFHL/uxmHtYIR3vSK+qlCld2An05U9VVICrPea0hvdGGnD0QV2TO4AF/VBebqA9jib1vq1JTVEVE9Vps3KY0HrZ3SH53kwQZG 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 Wed, Aug 20, 2025 at 03:52:22PM -0700, Boris Burkov wrote: [...] > > Thanks so much for the report and fix! I fear there might be some other > paths that try to get memcg from lruvec or folio or whatever without > checking it. I feel like in this exact case, I would want to go to the > first sign of trouble and fix it at lruvec_memcg(). But then who knows > what else we've missed. lruvec_memcg() is not an issue but folio_memcg() can be. I found following instances of folio_memcg() which are problematic (on next-20250819): mm/memcontrol.c:3246: css_get_many(&__folio_memcg(folio)->css, new_refs); include/trace/events/writeback.h:269: __entry->page_cgroup_ino = cgroup_ino(folio_memcg(folio)->css.cgroup); mm/workingset.c:244: struct mem_cgroup *memcg = folio_memcg(folio); mm/huge_memory.c:4020: WARN_ON_ONCE(!mem_cgroup_disabled() && !folio_memcg(folio)); > > May I ask what you were running to trigger this? My fstests run (clearly > not exercising enough interesting memory paths) did not hit it. > > This does make me wonder if the superior approach to the original patch > isn't just to go back to the very first thing Qu did and account these > to the root cgroup rather than do the whole uncharged thing. I don't have any strong preference one way or the other.