From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E2921C43334 for ; Wed, 6 Jul 2022 19:09:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233350AbiGFTJ1 (ORCPT ); Wed, 6 Jul 2022 15:09:27 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44138 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233270AbiGFTJ0 (ORCPT ); Wed, 6 Jul 2022 15:09:26 -0400 Received: from out1.migadu.com (out1.migadu.com [91.121.223.63]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A2F702316B for ; Wed, 6 Jul 2022 12:09:24 -0700 (PDT) Date: Wed, 6 Jul 2022 12:09:13 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1657134562; h=from:from:reply-to:subject:subject: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=ZrV9gZ3M7hyQBQVRJSRAAQW/nrB76C3hSoG3FLTFRhE=; b=BFx4o+Zn4HPzQFdHpfNqlMh1lYd1NMy8h3VaezauIwjA8OuK0rPGJaq4JEqFw05wcrijHP v/aI2kTB43TrYwvMPbf05pv+FKDJ5Jce9v5+CyGtGYT83lo1gGAjHRJ1/py93hMVbaSayb PS7K9X5SMbX5MJPFIlU6c5rYOyfVmYI= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Roman Gushchin To: Alexei Starovoitov Cc: Yafang Shao , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , Quentin Monnet , Hao Luo , bpf , linux-mm Subject: Re: [PATCH bpf-next v2 1/2] bpf: Make non-preallocated allocation low priority Message-ID: References: <20220706155848.4939-1-laoar.shao@gmail.com> <20220706155848.4939-2-laoar.shao@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Migadu-Auth-User: linux.dev Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Wed, Jul 06, 2022 at 09:47:32AM -0700, Alexei Starovoitov wrote: > On Wed, Jul 6, 2022 at 8:59 AM Yafang Shao wrote: > > > > GFP_ATOMIC doesn't cooperate well with memcg pressure so far, especially > > if we allocate too much GFP_ATOMIC memory. For example, when we set the > > memcg limit to limit a non-preallocated bpf memory, the GFP_ATOMIC can > > easily break the memcg limit by force charge. So it is very dangerous to > > use GFP_ATOMIC in non-preallocated case. One way to make it safe is to > > remove __GFP_HIGH from GFP_ATOMIC, IOW, use (__GFP_ATOMIC | > > __GFP_KSWAPD_RECLAIM) instead, then it will be limited if we allocate > > too much memory. > > > > We introduced BPF_F_NO_PREALLOC is because full map pre-allocation is > > too memory expensive for some cases. That means removing __GFP_HIGH > > doesn't break the rule of BPF_F_NO_PREALLOC, but has the same goal with > > it-avoiding issues caused by too much memory. So let's remove it. > > > > The force charge of GFP_ATOMIC was introduced in > > commit 869712fd3de5 ("mm: memcontrol: fix network errors from failing > > __GFP_ATOMIC charges") by checking __GFP_ATOMIC, then got improved in > > commit 1461e8c2b6af ("memcg: unify force charging conditions") by > > checking __GFP_HIGH (that is no problem because both __GFP_HIGH and > > __GFP_ATOMIC are set in GFP_AOMIC). So, if we want to fix it in memcg, > > we have to carefully verify all the callsites. Now that we can fix it in > > BPF, we'd better not modify the memcg code. > > > > This fix can also apply to other run-time allocations, for example, the > > allocation in lpm trie, local storage and devmap. So let fix it > > consistently over the bpf code > > > > __GFP_KSWAPD_RECLAIM doesn't cooperate well with memcg pressure neither > > currently. But the memcg code can be improved to make > > __GFP_KSWAPD_RECLAIM work well under memcg pressure if desired. > > Could you elaborate ? > > > It also fixes a typo in the comment. > > > > Signed-off-by: Yafang Shao > > Reviewed-by: Roman Gushchin > > Roman, do you agree with this change ? Yes, removing __GFP_HIGH makes sense to me. I can imagine we might want it for *some* bpf allocations, but applying it unconditionally looks wrong. Thanks!