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Wed, 12 Aug 2026 23:40:46 +0000 X-Migadu-Flow: FLOW_OUT Date: Wed, 12 Aug 2026 16:40:41 -0700 From: Shakeel Butt To: Andrew Morton 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: References: <20260811203203.3456029-1-shakeel.butt@linux.dev> <20260811203203.3456029-2-shakeel.butt@linux.dev> <20260812155010.8710b4a9191c9ee4ad6da255@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260812155010.8710b4a9191c9ee4ad6da255@linux-foundation.org> X-Rspam-User: X-Stat-Signature: gx3x7g5sm5iz744bscs91k84hnqkaq7o X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 8DDBE140002 X-HE-Tag: 1786578058-972728 X-HE-Meta: U2FsdGVkX19VttY0riEb3T0vemd80RmRxz+SNp85yKDrmEt668NZVjdecmhp4E4rbbKfvkJuDGPYMzAhfdtIkW7rchUgqcpJkHC+bmHJ4WLdfm0X+WFh0IIV8nZR7JSZNul234xpKDOrC3a+zo2AW6I5YzTWWdFnktF86VPi1SNgKbkZngSjPbgIxCRRKPwF0/jFECz4WOrXEIBTrQ/3zaI/9UF4UWvS1NCSnOMgMcZXaQbaLCOQ6X8B01t/SvnlRRxfOSl/bTy7/flD7h//H+iuJdsQ6uTteIklJAx4j59suLJ36VRjl1IZ+D00lRYtpvbkVjttkiCsIF4jMrPpoWnjxOl9bSjHVkflNelcEmYrLIkAP3XR4uUhi2XDbVHkQh9Pv6I3wcUw9rQZicoCj12/p+UZ+n5vPXf5DrCwJv0oxLg+RBFP83S2gm+xXy8A0YgMAeJaGO1R3B4PRNcw/x3CU5o0JjIBRItaJSzj5QVPZi3rvJpwiyG6yHXW7bvV1IrMVFfOz9irYJOv4xI0Y5f5UQ/bk0Wf1PetSzS+M5+5Q/Dr1QjjpqJZuc5YHJU8vazENRyk3Qn09llfeRtctFpntSmZBNhVValv7ajsRtmCVpYIOS2L2mldzdHpZ38GHTxVF6e8oETwsYCNO0M+H+9ZP9unBvJZPOcVSDiUgJaPM9CnSEKHLIuswRxeFKrj6qEOFhBu4T1zAha3n6itftkza8FPXMg8WtJjuiI86QMED07OhIfNB4buWI9EfINvyyMUq9cAQLghI+sH36NrZXURxVdOVqa0++GS6gurq0gspSld60RgybqQ6DNInS8MCgyYqrSp6gVNOcwHH236RZxGicicHMx/CnZJgkVFpE91i/856mQGMY+7ZUCuipPrPCVZlh4WJIZ5YrmieV74O/da4nHNzZ7L2IVmyW6QBjMpsvhPzMBz84yyC3e+Sw9ZUvnKev8Heb2O73gKOhC 2Ln9BAuC lVrvjGtrvamdemYCO2kUC0oPvbp3cirje9yPPxAZnmjW4wVtR7G7Tfb1AGVtN4f2aZ/Qet4B5Nr4yLzKqRNZRMb/R7Q9TKrLap/jyUEC5Y6loq1UoMIv5QVd8j/2Pc5+G8llZE5XDT2IuV1xRlyf6dc+OxE8w87HISyAvQm2HkpQkpo8nW2YAhlZE0VnY2iQ5sVIqlrG8I97kDd8GDlMnYTpZSOFbNbUsr7sYFy2bk5KVN4SKTliNT2/HQKhrY3VDSRemu27GKdlm9VRyUoaBk5Z6x83uqSb8q5+cGi0cwtzW4F0xXRqpSgwKetCFc+mwvOMAcUNp+2BStMDP8ToAFZbbF/SjNaVj0qOCNI2nLT6iPo6GxnqPIkuG1PvpCxsGJkY/TJj3uHC8TgcegPqZHO/ljFclUPXUsw3j+FuyZ3PPv8/mtQxX9Iny19oGbw1SMOZolRfC6pOeCS4= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Aug 12, 2026 at 03:50:10PM -0700, Andrew Morton wrote: > 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. Sounds good. > > It's old code, yes? Yes. > Are there any theories about why the sysbot issue > has just popped up? The reproducer is toggling MGLRU on and off continuosly which is not really recommended. > Should we backport the fix? I have no concerns in backporting this to older stable kernels.