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Sun, 15 Nov 2020 20:14:25 +0000 Received: from abhmp0001.oracle.com (abhmp0001.oracle.com [141.146.116.7]) by userv0121.oracle.com (8.14.4/8.13.8) with ESMTP id 0AFKEM4S015914; Sun, 15 Nov 2020 20:14:22 GMT Received: from localhost.localdomain (/10.211.9.80) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Sun, 15 Nov 2020 12:14:22 -0800 From: Dongli Zhang To: linux-mm@kvack.org, netdev@vger.kernel.org Cc: 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, akpm@linux-foundation.org, davem@davemloft.net, edumazet@google.com, vbabka@suse.cz, dongli.zhang@oracle.com Subject: [PATCH v3 1/1] page_frag: Recover from memory pressure Date: Sun, 15 Nov 2020 12:10:29 -0800 Message-Id: <20201115201029.11903-1-dongli.zhang@oracle.com> X-Mailer: git-send-email 2.17.1 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9806 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxscore=0 phishscore=0 bulkscore=0 adultscore=0 malwarescore=0 mlxlogscore=999 spamscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2011150130 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9806 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 phishscore=0 adultscore=0 priorityscore=1501 bulkscore=0 clxscore=1015 mlxlogscore=999 malwarescore=0 mlxscore=0 spamscore=0 lowpriorityscore=0 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2011150130 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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. References: https://lore.kernel.org/lkml/20201103193239.1807-1-dongli.zhang@oracle.com/ References: https://lore.kernel.org/linux-mm/20201105042140.5253-1-willy@infradead.org/ Suggested-by: Matthew Wilcox (Oracle) Cc: Aruna Ramakrishna Cc: Bert Barbe Cc: Rama Nichanamatlu Cc: Venkat Venkatsubra Cc: Manjunath Patil Cc: Joe Jin Cc: SRINIVAS Cc: stable@vger.kernel.org Fixes: 79930f5892e ("net: do not deplete pfmemalloc reserve") Signed-off-by: Dongli Zhang Acked-by: Vlastimil Babka Reviewed-by: Eric Dumazet --- Changed since v1: - change author from Matthew to Dongli - Add references to all prior discussions - Add more details to commit message Changed since v2: - add unlikely (suggested by Eric Dumazet) mm/page_alloc.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 23f5066bd4a5..91129ce75ed4 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -5103,6 +5103,11 @@ void *page_frag_alloc(struct page_frag_cache *nc, if (!page_ref_sub_and_test(page, nc->pagecnt_bias)) goto refill; + if (unlikely(nc->pfmemalloc)) { + free_the_page(page, compound_order(page)); + goto refill; + } + #if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE) /* if size can vary use size else just use PAGE_SIZE */ size = nc->size;