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d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=vCEF6wqc95cLrmB/oV3IZ67dACUQA3nyuwvULLWrblQ=; b=PbS0jdu3ji/F+d1+8fX9vwoK0K6UqOOXVMPi4W9UP2alDi9oGkx9QJpjhfMtRvmXMy pIT30lQoapDPkIMJvQbstkOobcl7Zz5tEVCizMe+wDypDQY6/TQoskeqwuvCKRFpSrX7 HwR3AZrFvPa9H7LBT04HCkuiEvlKRVbI+vhXsxlg0a3nOX3JurZ9vIIktMgt52dvym8B cD9Fl7wPELmzVBvffuUwAuc91V6mFFxFMz6oCCnQnccDIyr24h9oJD9j/2d0PYs7d2B+ uvjEp0u7IFVogdjznV/hevaR6QHABt8p2dpQDlPTvC6rGGAnH9F0QP7i4wrRzW2gQsAN EXeg== X-Gm-Message-State: AOAM532MqsmnFVaLDK7AV/06KuLJBng2WEYIEu18DaZEZk9L7lkncf9B JJVjA0Cqp3/5zLTjBzVDs7tYmaR/3YFcPfNMyD3oMg== X-Google-Smtp-Source: ABdhPJxAavBApZLnZJgIBEBEUhAPqDcRk1LqV3Ve1UUvn7RINl0zO9IW1qjmCcY+90sQgwoIJdCILpT6JoB2i1iB490= X-Received: by 2002:a2e:96c3:: with SMTP id d3mr2526801ljj.270.1598049712869; Fri, 21 Aug 2020 15:41:52 -0700 (PDT) MIME-Version: 1.0 References: <20200821212056.3769116-1-guro@fb.com> In-Reply-To: <20200821212056.3769116-1-guro@fb.com> From: Shakeel Butt Date: Fri, 21 Aug 2020 15:41:41 -0700 Message-ID: Subject: Re: [PATCH] mm: rework remote memcg charging API to support nesting To: Roman Gushchin Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Linux MM , Kernel Team , LKML , Dan Schatzberg Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 2C7FC1A4A0 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam01 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000148, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Aug 21, 2020 at 2:21 PM Roman Gushchin wrote: > > Currently the remote memcg charging API consists of two functions: > memalloc_use_memcg() and memalloc_unuse_memcg(), which set and clear > the memcg value, which overwrites the memcg of the current task. > > memalloc_use_memcg(target_memcg); > <...> > memalloc_unuse_memcg(); > > It works perfectly for allocations performed from a normal context, > however an attempt to call it from an interrupt context or just nest > two remote charging blocks will lead to an incorrect accounting. > On exit from the inner block the active memcg will be cleared > instead of being restored. > > memalloc_use_memcg(target_memcg); > > memalloc_use_memcg(target_memcg_2); > <...> > memalloc_unuse_memcg(); > > Error: allocation here are charged to the memcg of the current > process instead of target_memcg. > > memalloc_unuse_memcg(); > > This patch extends the remote charging API by switching to a single > function: struct mem_cgroup *set_active_memcg(struct mem_cgroup *memcg), > which sets the new value and returns the old one. So a remote charging > block will look like: > > old_memcg = set_active_memcg(target_memcg); > <...> > set_active_memcg(old_memcg); > > This patch is heavily based on the patch by Johannes Weiner, > which can be found here: https://lkml.org/lkml/2020/5/28/806 . > > Signed-off-by: Roman Gushchin > Cc: Johannes Weiner > Cc: Shakeel Butt > Cc: Dan Schatzberg Reviewed-by: Shakeel Butt