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=-13.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_IN_DEF_DKIM_WL autolearn=no 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 ED01AC433E0 for ; Thu, 14 Jan 2021 12:53:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B1FA023A58 for ; Thu, 14 Jan 2021 12:53:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727163AbhANMwn (ORCPT ); Thu, 14 Jan 2021 07:52:43 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44012 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726891AbhANMwm (ORCPT ); Thu, 14 Jan 2021 07:52:42 -0500 Received: from mail-qk1-x735.google.com (mail-qk1-x735.google.com [IPv6:2607:f8b0:4864:20::735]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8A12CC061575 for ; Thu, 14 Jan 2021 04:51:56 -0800 (PST) Received: by mail-qk1-x735.google.com with SMTP id p14so7480462qke.6 for ; Thu, 14 Jan 2021 04:51:56 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=b0xwzUQ09tQNNwHy+qgRNeihhGrvkVw2IceHHCVee2s=; b=rVpL7l0BbhnTd+dgj69NKSfaqOPMz1TQEKO/BxztQi257jHhLSVhhnMCAJMIzbe8gQ l2ExqJb3dT6JIOD2FvhWiH8GhokBKkpFSGi5Jtwc9pb4cON15WjNzSImVliRBDZZgmsm Hy/vE0rW9VsT49cQZeLRMrSBKg8NX+4UDa4Sa6uzRKCLVqNozo3cuP7elccVeBnnkMVU rnUlQvNpuh7UI56kwO8JpuRRvfuW46SVkqixs95bgpyqWNa8OayAzQsslSxit1aiEjMn gA1aldEqQbaEFNDFbCypRMVdCsttM4VsCxXI7pE4kz102YZNtOjk6sjvIPZg9AA2Tjf1 3bzA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=b0xwzUQ09tQNNwHy+qgRNeihhGrvkVw2IceHHCVee2s=; b=pa7G8ZBlETO73M+rg2EWZCvOgzsMDheUwCJFYN+fDMKSNLBS2swPzfuOs7YK1x6bs6 DqFQ10VgtuScAI56KYhT930Cu6k7z0mRJ9RIKbT3KtHsTaHYNqRUSKjj/msrI6Yay9bT VJFLBdWAadQYWJ4Q8I74K31CVFyfH3mVi43x0wiF86A5DifcaF9tDAXB9eJb0GcPRPQu NVwjY8r2My8uL4Y/MYz3ragqq/keG58+7w3TPwMVm/+hyUCa32CnWTmboea4uXxa4b8E Usk0mbDhwaqzPlUmsLNlrioGumauq75lAPbNYH8IC6k2j1AAhnFFyao6Y7oJWQ1WLKyt WOIQ== X-Gm-Message-State: AOAM5307s7BtzUf7SuRVbKWkkJCrdeWSTtvGELi1pTJzWnM0L8+Ghd5Q Tm2Mj9sfMhFog5VZ6+JultrFS29OWXzPzGw77d6wWw== X-Google-Smtp-Source: ABdhPJx4sjovkawAsnpLFh1+NJnbj+8WF6kWyKSTayfll58A+yzIphC6v80dijrA63uft2t1RSpuCliMHoN9j5GkyVU= X-Received: by 2002:a37:9a97:: with SMTP id c145mr6769847qke.350.1610628715515; Thu, 14 Jan 2021 04:51:55 -0800 (PST) MIME-Version: 1.0 References: <20210113133523.39205-1-alobakin@pm.me> <20210113133635.39402-1-alobakin@pm.me> <20210113133635.39402-2-alobakin@pm.me> <20210114114046.7272-1-alobakin@pm.me> <20210114124406.9049-1-alobakin@pm.me> In-Reply-To: From: Dmitry Vyukov Date: Thu, 14 Jan 2021 13:51:44 +0100 Message-ID: Subject: Re: [PATCH v2 net-next 2/3] skbuff: (re)use NAPI skb cache on allocation path To: Alexander Lobakin Cc: Eric Dumazet , "David S. Miller" , Jakub Kicinski , Edward Cree , Jonathan Lemon , Willem de Bruijn , Miaohe Lin , Steffen Klassert , Guillaume Nault , Yadu Kishore , Al Viro , netdev , LKML Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Thu, Jan 14, 2021 at 1:50 PM Dmitry Vyukov wrote: > > On Thu, Jan 14, 2021 at 1:44 PM Alexander Lobakin wrote: > > > > From: Dmitry Vyukov > > Date: Thu, 14 Jan 2021 12:47:31 +0100 > > > > > On Thu, Jan 14, 2021 at 12:41 PM Alexander Lobakin wrote: > > >> > > >> From: Eric Dumazet > > >> Date: Wed, 13 Jan 2021 15:36:05 +0100 > > >> > > >>> On Wed, Jan 13, 2021 at 2:37 PM Alexander Lobakin wrote: > > >>>> > > >>>> Instead of calling kmem_cache_alloc() every time when building a NAPI > > >>>> skb, (re)use skbuff_heads from napi_alloc_cache.skb_cache. Previously > > >>>> this cache was only used for bulk-freeing skbuff_heads consumed via > > >>>> napi_consume_skb() or __kfree_skb_defer(). > > >>>> > > >>>> Typical path is: > > >>>> - skb is queued for freeing from driver or stack, its skbuff_head > > >>>> goes into the cache instead of immediate freeing; > > >>>> - driver or stack requests NAPI skb allocation, an skbuff_head is > > >>>> taken from the cache instead of allocation. > > >>>> > > >>>> Corner cases: > > >>>> - if it's empty on skb allocation, bulk-allocate the first half; > > >>>> - if it's full on skb consuming, bulk-wipe the second half. > > >>>> > > >>>> Also try to balance its size after completing network softirqs > > >>>> (__kfree_skb_flush()). > > >>> > > >>> I do not see the point of doing this rebalance (especially if we do not change > > >>> its name describing its purpose more accurately). > > >>> > > >>> For moderate load, we will have a reduced bulk size (typically one or two). > > >>> Number of skbs in the cache is in [0, 64[ , there is really no risk of > > >>> letting skbs there for a long period of time. > > >>> (32 * sizeof(sk_buff) = 8192) > > >>> I would personally get rid of this function completely. > > >> > > >> When I had a cache of 128 entries, I had worse results without this > > >> function. But seems like I forgot to retest when I switched to the > > >> original size of 64. > > >> I also thought about removing this function entirely, will test. > > >> > > >>> Also it seems you missed my KASAN support request ? > > >> I guess this is a matter of using kasan_unpoison_range(), we can ask for help. > > >> > > >> I saw your request, but don't see a reason for doing this. > > >> We are not caching already freed skbuff_heads. They don't get > > >> kmem_cache_freed before getting into local cache. KASAN poisons > > >> them no earlier than at kmem_cache_free() (or did I miss someting?). > > >> heads being cached just get rid of all references and at the moment > > >> of dropping to the cache they are pretty the same as if they were > > >> allocated. > > > > > > KASAN should not report false positives in this case. > > > But I think Eric meant preventing false negatives. If we kmalloc 17 > > > bytes, KASAN will detect out-of-bounds accesses beyond these 17 bytes. > > > But we put that data into 128-byte blocks, KASAN will miss > > > out-of-bounds accesses beyond 17 bytes up to 128 bytes. > > > The same holds for "logical" use-after-frees when object is free, but > > > not freed into slab. > > > > > > An important custom cache should use annotations like > > > kasan_poison_object_data/kasan_unpoison_range. > > > > As I understand, I should > > kasan_poison_object_data(skbuff_head_cache, skb) and then > > kasan_unpoison_range(skb, sizeof(*skb)) when putting it into the > > cache? > > I think it's the other way around. It should be _un_poisoned when used. > If it's fixed size, then unpoison_object_data should be a better fit: > https://elixir.bootlin.com/linux/v5.11-rc3/source/mm/kasan/common.c#L253 Variable-size poisoning/unpoisoning would be needed for the skb data itself: https://bugzilla.kernel.org/show_bug.cgi?id=199055