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From: Shakeel Butt To: Michal Hocko Cc: Andrew Morton , Johannes Weiner , Roman Gushchin , Muchun Song , Hugh Dickins , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-doc@vger.kernel.org, Meta kernel team Subject: Re: [RFC PATCH 3/3] memcg-v1: remove memcg move locking code Message-ID: References: <20241024065712.1274481-1-shakeel.butt@linux.dev> <20241024065712.1274481-4-shakeel.butt@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Stat-Signature: o8bxpcxd3msff71cix144ktwnqoypwkz X-Rspamd-Queue-Id: 21526100014 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1729790618-233606 X-HE-Meta: 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 /7IdpEY/ Vb9JsYr/4NkbzA0NYndo31uvYXV41jq0ctc8/wVHfPevkrS896U9Ul3ML4vAyxDNkozgHMn0CluiB1LBHLYNOR+iuzaA5mYLnRt5B2xnrROAkOv006XfAIQofTmAnwTLV2fulMfJQG9Z+V3NCirlao2Id4A== 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 Thu, Oct 24, 2024 at 11:16:52AM GMT, Michal Hocko wrote: > On Wed 23-10-24 23:57:12, Shakeel Butt wrote: > > The memcg v1's charge move feature has been deprecated. There is no need > > to have any locking or protection against the moving charge. Let's > > proceed to remove all the locking code related to charge moving. > > > > Signed-off-by: Shakeel Butt > > --- > > -/** > > - * folio_memcg_lock - Bind a folio to its memcg. > > - * @folio: The folio. > > - * > > - * This function prevents unlocked LRU folios from being moved to > > - * another cgroup. > > - * > > - * It ensures lifetime of the bound memcg. The caller is responsible > > - * for the lifetime of the folio. > > - */ > > -void folio_memcg_lock(struct folio *folio) > > -{ > > - struct mem_cgroup *memcg; > > - unsigned long flags; > > - > > - /* > > - * The RCU lock is held throughout the transaction. The fast > > - * path can get away without acquiring the memcg->move_lock > > - * because page moving starts with an RCU grace period. > > - */ > > - rcu_read_lock(); > > Is it safe to remove the implicit RCU? Good question. I think it will be safe to keep the RCU in this patch and in the followup examine each place and decide to remove RCU or not. Thanks for the review.