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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1uoCN1-0000000F0kr-0WSI; Tue, 19 Aug 2025 02:46:43 +0000 Date: Tue, 19 Aug 2025 03:46:42 +0100 From: Matthew Wilcox To: Boris Burkov Cc: akpm@linux-foundation.org, linux-btrfs@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, kernel-team@fb.com, shakeel.butt@linux.dev, wqu@suse.com, 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <43fed53d45910cd4fa7a71d2e92913e53eb28774.1755562487.git.boris@bur.io> X-Stat-Signature: q4nse4otfaai5wea7ysamtnddz8cgxoe X-Rspam-User: X-Rspamd-Queue-Id: D98DB40008 X-Rspamd-Server: rspam01 X-HE-Tag: 1755571605-753306 X-HE-Meta: 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 B8qnowk8 bCbdh6CA7kwd37ux99W9Mzhz73jzp3aBL02Vsj6oH/bWxxrFrdxty7IpuOs7HwIDR+WtHJGp73Fh9Fh7FgXcxKZVqHvczV4xb31tuhuKq8u4+NM3hHuLvJR2ja5Jq38fnnE2F7SQvqRaZSuaXPhyeB2+/A6jnaSgJc2qGt+Z7AuDCzeDbuqvZ8X85GPl9F3QyWVcHj85RB1kqcdOYczXzcJUJ0GRbxTXZslV0 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 Mon, Aug 18, 2025 at 05:36:53PM -0700, Boris Burkov wrote: > +++ b/mm/filemap.c > @@ -960,15 +960,19 @@ int filemap_add_folio(struct address_space *mapping, struct folio *folio, > { > void *shadow = NULL; > int ret; > + bool charge_mem_cgroup = !test_bit(AS_UNCHARGED, &mapping->flags); > > - ret = mem_cgroup_charge(folio, NULL, gfp); > - if (ret) > - return ret; > + if (charge_mem_cgroup) { > + ret = mem_cgroup_charge(folio, NULL, gfp); > + if (ret) > + return ret; > + } > > __folio_set_locked(folio); > ret = __filemap_add_folio(mapping, folio, index, gfp, &shadow); > if (unlikely(ret)) { > - mem_cgroup_uncharge(folio); > + if (charge_mem_cgroup) > + mem_cgroup_uncharge(folio); > __folio_clear_locked(folio); This is unnecessarily complex; mem_cgroup_uncharge() is a no-op if the folio is not charged. Sure, it's a wasted function call, but this is a rare error path, so minimising size is more important than minimising time. So you can drop the 'bool' as well: + if (!test_bit(AS_UNCHARGED, &mapping->flags)) {