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=-6.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 1D1D7C56202 for ; Wed, 18 Nov 2020 19:47:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AF40B246A6 for ; Wed, 18 Nov 2020 19:47:19 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="lHosobLo" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726463AbgKRTq6 (ORCPT ); Wed, 18 Nov 2020 14:46:58 -0500 Received: from mail.kernel.org ([198.145.29.99]:40464 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726357AbgKRTq5 (ORCPT ); Wed, 18 Nov 2020 14:46:57 -0500 Received: from kicinski-fedora-PC1C0HJN.hsd1.ca.comcast.net (unknown [163.114.132.5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id F094A246AA; Wed, 18 Nov 2020 19:46:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1605728816; bh=r4rtZMhdAiBSx+HYth3NByAdBaTUCKCee8fL0I2kNRA=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=lHosobLoK22MXnVs0MjQ4ibqeRWzsM41/a6EmjFHtqfruDDk9og6FzvPaO2faW0zv jQOzL9YbAkVIz/w2o10YIQlrnodjuJmvIEddKJIog1qKb02XCdvby4FWQi8+pJ4hnn FJxAwQkeq4Ut9VCw2cr3TAjjTkzgoyf5DvczvGq4= Date: Wed, 18 Nov 2020 11:46:54 -0800 From: Jakub Kicinski To: akpm@linux-foundation.org Cc: Dongli Zhang , linux-mm@kvack.org, netdev@vger.kernel.org, willy@infradead.org, aruna.ramakrishna@oracle.com, bert.barbe@oracle.com, rama.nichanamatlu@oracle.com, venkat.x.venkatsubra@oracle.com, manjunath.b.patil@oracle.com, joe.jin@oracle.com, srinivas.eeda@oracle.com, stable@vger.kernel.org, linux-kernel@vger.kernel.org, davem@davemloft.net, edumazet@google.com, vbabka@suse.cz Subject: Re: [PATCH v3 1/1] page_frag: Recover from memory pressure Message-ID: <20201118114654.3435f76c@kicinski-fedora-PC1C0HJN.hsd1.ca.comcast.net> In-Reply-To: <20201115201029.11903-1-dongli.zhang@oracle.com> References: <20201115201029.11903-1-dongli.zhang@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Sun, 15 Nov 2020 12:10:29 -0800 Dongli Zhang wrote: > The ethernet driver may allocate skb (and skb->data) via napi_alloc_skb(). > This ends up to page_frag_alloc() to allocate skb->data from > page_frag_cache->va. > > During the memory pressure, page_frag_cache->va may be allocated as > pfmemalloc page. As a result, the skb->pfmemalloc is always true as > skb->data is from page_frag_cache->va. The skb will be dropped if the > sock (receiver) does not have SOCK_MEMALLOC. This is expected behaviour > under memory pressure. > > However, once kernel is not under memory pressure any longer (suppose large > amount of memory pages are just reclaimed), the page_frag_alloc() may still > re-use the prior pfmemalloc page_frag_cache->va to allocate skb->data. As a > result, the skb->pfmemalloc is always true unless page_frag_cache->va is > re-allocated, even if the kernel is not under memory pressure any longer. > > Here is how kernel runs into issue. > > 1. The kernel is under memory pressure and allocation of > PAGE_FRAG_CACHE_MAX_ORDER in __page_frag_cache_refill() will fail. Instead, > the pfmemalloc page is allocated for page_frag_cache->va. > > 2: All skb->data from page_frag_cache->va (pfmemalloc) will have > skb->pfmemalloc=true. The skb will always be dropped by sock without > SOCK_MEMALLOC. This is an expected behaviour. > > 3. Suppose a large amount of pages are reclaimed and kernel is not under > memory pressure any longer. We expect skb->pfmemalloc drop will not happen. > > 4. Unfortunately, page_frag_alloc() does not proactively re-allocate > page_frag_alloc->va and will always re-use the prior pfmemalloc page. The > skb->pfmemalloc is always true even kernel is not under memory pressure any > longer. > > Fix this by freeing and re-allocating the page instead of recycling it. Andrew, are you taking this via -mm or should I put it in net? I'm sending a PR to Linus tomorrow.