From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9177C36AEE; Wed, 20 Sep 2023 13:47:39 +0000 (UTC) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id D8C71200A3; Wed, 20 Sep 2023 13:47:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1695217657; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=S/snCuZpEV/rtAoiDV8eTkiFsU9tul7/5xeWIzs69P4=; b=SieMIAkivNWy3EVUvOjPG5/PORQlkKhXDFby+/Llv1MT4g5OqJjZL+SnRmLeRk5vzysjdf wg8/6w1A5jKCofvAFHe8UMJaBGMF4YlAWwKFVeAWKQZtcUNErEikKd/i0mpm6rl3gF5NU4 waD4aVwTbnXNUjHh/k0mM5kmMD99RRM= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id B50D71333E; Wed, 20 Sep 2023 13:47:37 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id p93hKfn3CmVNCwAAMHmgww (envelope-from ); Wed, 20 Sep 2023 13:47:37 +0000 Date: Wed, 20 Sep 2023 15:47:37 +0200 From: Michal Hocko To: Jeremi Piotrowski , Shakeel Butt , Johannes Weiner , Roman Gushchin , Muchun Song Cc: Greg Kroah-Hartman , stable@vger.kernel.org, patches@lists.linux.dev, Tejun Heo , Andrew Morton , linux-kernel@vger.kernel.org, regressions@lists.linux.dev, mathieu.tortuyaux@gmail.com Subject: Re: [REGRESSION] Re: [PATCH 6.1 033/219] memcg: drop kmem.limit_in_bytes Message-ID: References: <20230917191040.964416434@linuxfoundation.org> <20230917191042.204185566@linuxfoundation.org> <20230920081101.GA12096@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net> <101987a1-b1ab-429d-af03-b6bdf6216474@linux.microsoft.com> <4eb47d6a-b127-4aad-af30-896c3b9505b4@linux.microsoft.com> Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4eb47d6a-b127-4aad-af30-896c3b9505b4@linux.microsoft.com> On Wed 20-09-23 15:25:23, Jeremi Piotrowski wrote: > On 9/20/2023 1:07 PM, Michal Hocko wrote: [...] > > I mean, normally I would be just fine reverting this API change because > > it is disruptive but the only way to have the file available and not > > break somebody is to revert 58056f77502f ("memcg, kmem: further > > deprecate kmem.limit_in_bytes") as well. Or to ignore any value written > > there but that sounds rather dubious. Although one could argue this > > would mimic nokmem kernel option. > > > > I just want to make sure we don't introduce yet another new behavior in this legacy > system. I have not seen breakage due to 58056f77502f. Mimicing nokmem sounds good but > does this mean "don't enforce limits" (that should be fine) or "ignore writes to the limit" > (=don't event store the written limit). The latter might have unintended consequences. Yes it would mean that the limit is never enforced. Bad as it is the thing is that the hard limit on kernel memory is broken by design and unfixable. This causes all sorts of unexpected kernel allocation failures that this is simply unsafe to use. All that being said I can see the following options 1) keep the current upstream status and not export the file 2) revert both 58056f77502f and 86327e8eb94 and make it clear that kmem.limit_in_bytes is unsupported so failures or misbehavior as a result of the limit being hit are likely not going to be investigated or fixed. 3) reverting like in 2) but never inforce the limit (so basically nokmem semantic) Shakeel, Johannes, Roman, Muchun Song what do you think? -- Michal Hocko SUSE Labs