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h=Date:From:To:Cc:Subject:In-Reply-To:References; b=qZP2/twoQ3M6TVc5K/4I1BejDEiVV/5s1xxUZWr+68fh1f4NGuze+uNFmhKGphuwS IDWzhDdhQucWY5qGffH0ue8tsfYipYzw11nEWRJfDAk1JemHr5cN6Ug+Ox+bZbNgOt GBZUmjLQXGzvtRqw8eYb/ANowk9aWXMTDNKByUmM= Date: Wed, 12 Aug 2026 15:50:10 -0700 From: Andrew Morton To: Shakeel Butt Cc: Michal Hocko , Johannes Weiner , Roman Gushchin , Muchun Song , David Hildenbrand , Lorenzo Stoakes , Kairui Song , Qi Zheng , Barry Song , Axel Rasmussen , Meta kernel team , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, syzbot+12ee2725d5fde63a9c96@syzkaller.appspotmail.com Subject: Re: [PATCH 1/9] memcg: make the v1 soft limit knob inert Message-Id: <20260812155010.8710b4a9191c9ee4ad6da255@linux-foundation.org> In-Reply-To: <20260811203203.3456029-2-shakeel.butt@linux.dev> References: <20260811203203.3456029-1-shakeel.butt@linux.dev> <20260811203203.3456029-2-shakeel.butt@linux.dev> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 375E720004 X-Rspamd-Server: rspam10 X-Rspam-User: X-Stat-Signature: n6hifj5534dyncqy44hwhpag8iuf69cx X-HE-Tag: 1786575012-687480 X-HE-Meta: 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 MWwTHSL1 0MmZQnnN9kitchDPF3i6kNCJfp73o8E7cj8S9bAdH66NgofH1zbCPG/XtO3nFL0gLTuzbJgIMm/Fk5D+aWOHOVrW5TenGUTHyJVrovXw8hJurHTpQbRGtenN0IjahvUiAiPSu6Sw9hTn1Q123GG1eaC9lEHKWPsR9PZfUdxfcu8xw8/4IP5L2K9O77+iqGmpIGCpL8FBXrHYSkL6sSRqoGv1NwtukStS/Jjw233oIVdCFNa98J9Y+N8SeVOuepjIlrizfx9qMKi962Yl4emPd4zCMZp5X7+9QuVLYldE5jXVIHzN69qaCu0DM2tCydFFMyHWRHgHJUm3hL1TIUy6uTh4Yn4qNizvJmcOyOB4AffmMegneBN3bMNOUY3zMsmaFJVt6 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, 11 Aug 2026 13:31:55 -0700 Shakeel Butt wrote: > The v1 soft limit has been deprecated since v6.12 and nobody has > reported depending on it. Start the removal by decoupling the interface > from the implementation: keep memory.soft_limit_in_bytes, but ignore > writes to it and always report the maximum value on read similar to > what memory.kmem.limit_in_bytes already does. > > Writes are still parsed, so malformed input keeps returning -EINVAL. > The knob now also behaves the same everywhere: it used to return > -EOPNOTSUPP on PREEMPT_RT, where soft limit reclaim has always been > disabled. > > This also fixes the syzbot report linked below. Soft limit reclaim is > the only caller that runs shrink_lruvec() from kswapd against a > specific memcg, so it is the only way to reach lru_gen_shrink_lruvec() > and in turn set_mm_walk(), which warns when called from kswapd. Thanks, I'll pluck this one as a hotfix. It's old code, yes? Are there any theories about why the sysbot issue has just popped up? Should we backport the fix?