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Sat, 05 Sep 2026 01:47:42 +0000 X-Mizu-Trace-ID: 6a96a44c2aaa9fd1 X-Migadu-Flow: FLOW_OUT Date: Fri, 4 Sep 2026 18:47:41 -0700 From: Shakeel Butt To: Joshua Hahn Cc: hannes@cmpxchg.org, mhocko@kernel.org, roman.gushchin@linux.dev, muchun.song@linux.dev, akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, dev@lankhorst.se, mripard@kernel.org, nat@pixelcluster.dev, tj@kernel.org, mkoutny@suse.com, osalvador@suse.de, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, kernel-team@meta.com Subject: Re: [PATCH v5 2/7] mm/page_counter: report the number of pages charged Message-ID: References: <20260831163752.2193337-1-joshua.hahnjy@gmail.com> <20260831163752.2193337-3-joshua.hahnjy@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260831163752.2193337-3-joshua.hahnjy@gmail.com> X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 73412180004 X-Stat-Signature: b9t9ie54u6id6ejthfwq9d3go3887acr X-HE-Tag: 1788572866-838441 X-HE-Meta: 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 YH/yx/p/ JAmijp7r2S3qJice8acGppLPb5Fzz3a/0ZjjWzUE13C4S6C9TLNRsirQoHtmgE4Na6c18x4nYUhQ1eFqZVKCCSvt1nmay97yOZyxD2p+AyOSnJ64J69xaq0eiQ8Ks9Ybrn9lP3t9xIQBVWvVuklg4aYv6A+fxY+l2me60QKFNATxszQdj11CcUE7/XjM9q7lzzSMjJc6uWnafPc7mhIAV6mMY72d1t8Pv/G8vQxO6Egl1dl6JKM1zENC8hWnDxs+yfcKligtLD0x56+ql/rhuwbj7p/BfCXEM7Md+h/rQpYPu7zwd0ZTgIX3ut9SiUE4TehhlwbBokrL5mrXoaKo9S68fq/Veb1SyBJeqBtH0vlpkSrRHOhRcTdsDDIGjDDYR3gDY/Wx1pI6QXhs= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Aug 31, 2026 at 09:37:46AM -0700, Joshua Hahn wrote: > Add an optional @nr_charged parameter to page_counter_try_charge. > On success, it will be set to the number of pages actually charged to > the hierarchy. Today this number is always @nr_pages, so there is no > functional change. > > Of the 6 callsites, only one user (try_charge_memcg) uses that > information. The number of charged pages is added to > current->memcg_nr_pages_over_high to indicate how many pages it charged > to the hierarchy while over high. > > Today, try_charge_memcg requests "batch" from page_counter_try_charge > and adds that same amount to memcg_nr_pages_over_high on success, since > page_counter_try_charge's only source of charges is the hierarchy. > However, this invariant changes later in the series when stock is pushed > down from the memcg level to the page_counter level, and a page_counter > charge can be successful without growing the hierarchy size. > > Plumb the new parameter to all callsites, passing NULL where the source > of charge does not matter to the caller, and passing &nr_charged in > try_charge_memcg to account the hierarchy size growth. The terminology of "growing the hierarchy size" and "hierarchy size growth" is confusing. The code looks fine.