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 X-Spam-Level: X-Spam-Status: No, score=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,USER_AGENT_MUTT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D8C8BC4360F for ; Mon, 18 Mar 2019 15:39:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A767F20854 for ; Mon, 18 Mar 2019 15:39:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1552923588; bh=WYFm/lIcbWgcnfwIVi5+MM/QMWgOl4XFh5Y8katOEp4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=HOaB3pAHt+2h0k+wMN4A+uOGsBjeACxPdvE+YjKBhR0UYt4xSRxA35rXYofnzihha jsTVyBFfbh2FBMCil+MMHF3VF9WPtZCvljFrh4ihlDGv8cLDQjk5o7DBS+LkqOl7OX U+9SS7IM8uGcgNSoyO0UaiC5Epvg11pw4lsl+7Xw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727487AbfCRPjr (ORCPT ); Mon, 18 Mar 2019 11:39:47 -0400 Received: from mx2.suse.de ([195.135.220.15]:43086 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726808AbfCRPjr (ORCPT ); Mon, 18 Mar 2019 11:39:47 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id BAC35AED5; Mon, 18 Mar 2019 15:39:44 +0000 (UTC) Date: Mon, 18 Mar 2019 16:39:40 +0100 From: Michal Hocko To: Martynas Pumputis Cc: netdev@vger.kernel.org, bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net, Yonghong Song Subject: Re: [PATCH v3 bpf] bpf: Try harder when allocating memory for large maps Message-ID: <20190318153940.GL8924@dhcp22.suse.cz> References: <20190318151026.21539-1-m@lambda.lt> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190318151026.21539-1-m@lambda.lt> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Mon 18-03-19 16:10:26, Martynas Pumputis wrote: > It has been observed that sometimes a higher order memory allocation > for BPF maps fails when there is no obvious memory pressure in a system. > > E.g. the map (BPF_MAP_TYPE_LRU_HASH, key=38, value=56, max_elems=524288) > could not be created due to vmalloc unable to allocate 75497472B, > when the system's memory consumption (in MB) was the following: > > Total: 3942 Used: 837 (21.24%) Free: 138 Buffers: 239 Cached: 2727 > > Later analysis [1] by Michal Hocko showed that the vmalloc was not trying > to reclaim memory from the page cache and was failing prematurely due to > __GFP_NORETRY. > > Considering dcda9b0471 ("mm, tree wide: replace __GFP_REPEAT by > __GFP_RETRY_MAYFAIL with more useful semantic") and [1], we can replace > __GFP_NORETRY with __GFP_RETRY_MAYFAIL, as it won't invoke OOM killer > and will try harder to fulfil allocation requests. > > Unfortunately, replacing the body of the BPF map memory allocation > function with the kvmalloc_node helper function is not an option at this > point in time, given 1) kmalloc is non-optional for higher order > allocations, and 2) passing __GFP_RETRY_MAYFAIL to the kmalloc would stress > the slab allocator too much for large requests. > Thanks for extending the changelog! > The change has been tested with the workloads mentioned above and by > observing oom_kill value from /proc/vmstat. > > [1]: https://lore.kernel.org/bpf/20190310071318.GW5232@dhcp22.suse.cz/ > > Acked-by: Yonghong Song > Signed-off-by: Martynas Pumputis The patch looks good to me from the allocator usage POV. I wish there was a good way to give you a util function to use rather than opencoding but this is the only place with this semantic I have seen and I am not sure it is generic enough. Let's see what the future has to tell us. > --- > kernel/bpf/syscall.c | 22 +++++++++++++++------- > 1 file changed, 15 insertions(+), 7 deletions(-) > > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c > index 62f6bced3a3c..afca36f53c49 100644 > --- a/kernel/bpf/syscall.c > +++ b/kernel/bpf/syscall.c > @@ -136,21 +136,29 @@ static struct bpf_map *find_and_alloc_map(union bpf_attr *attr) > > void *bpf_map_area_alloc(size_t size, int numa_node) > { > - /* We definitely need __GFP_NORETRY, so OOM killer doesn't > - * trigger under memory pressure as we really just want to > - * fail instead. > + /* We really just want to fail instead of triggering OOM killer > + * under memory pressure, therefore we set __GFP_NORETRY to kmalloc, > + * which is used for lower order allocation requests. > + * > + * It has been observed that higher order allocation requests done by > + * vmalloc with __GFP_NORETRY being set might fail due to not trying > + * to reclaim memory from the page cache, thus we set > + * __GFP_RETRY_MAYFAIL to avoid such situations. > */ > - const gfp_t flags = __GFP_NOWARN | __GFP_NORETRY | __GFP_ZERO; > + > + const gfp_t flags = __GFP_NOWARN | __GFP_ZERO; > void *area; > > if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER)) { > - area = kmalloc_node(size, GFP_USER | flags, numa_node); > + area = kmalloc_node(size, GFP_USER | __GFP_NORETRY | flags, > + numa_node); > if (area != NULL) > return area; > } > > - return __vmalloc_node_flags_caller(size, numa_node, GFP_KERNEL | flags, > - __builtin_return_address(0)); > + return __vmalloc_node_flags_caller(size, numa_node, > + GFP_KERNEL | __GFP_RETRY_MAYFAIL | > + flags, __builtin_return_address(0)); > } > > void bpf_map_area_free(void *area) > -- > 2.21.0 > -- Michal Hocko SUSE Labs