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=-16.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 EC000C433B4 for ; Sun, 2 May 2021 18:08:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C3145611AB for ; Sun, 2 May 2021 18:08:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232392AbhEBSJf (ORCPT ); Sun, 2 May 2021 14:09:35 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:41283 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232363AbhEBSJe (ORCPT ); Sun, 2 May 2021 14:09:34 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1619978921; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:in-reply-to:in-reply-to:references:references; bh=kEFyh88t8RjL4Ya/tUcmCMYYCtAJ4jkovquK5V2cmso=; b=ZerIt5R+MVsZ06BNy13VlnPNW9HpjJqVswSmBbFdlqJcNDucTrfNSgOl8bHCTszi8HIvnr APYdJDDDwyazFyXMeivVIHqYAHG9WZgG71PSVFLVTpwEFxnRfq/iMlYmlsrbjkr2TYchuh sm7jkr2RU/KoqaKvIxc0/27tNnm644c= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-435-TArhv3WIP_WJue1uC6L8Ug-1; Sun, 02 May 2021 14:08:40 -0400 X-MC-Unique: TArhv3WIP_WJue1uC6L8Ug-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E89E2107ACC7; Sun, 2 May 2021 18:08:37 +0000 (UTC) Received: from llong.com (ovpn-112-236.rdu2.redhat.com [10.10.112.236]) by smtp.corp.redhat.com (Postfix) with ESMTP id 40BDE19D7D; Sun, 2 May 2021 18:08:36 +0000 (UTC) From: Waiman Long To: Johannes Weiner , Michal Hocko , Vladimir Davydov , Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Vlastimil Babka , Roman Gushchin , Shakeel Butt Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, Waiman Long Subject: [PATCH 2/2] mm: memcg/slab: Don't create unfreeable slab Date: Sun, 2 May 2021 14:07:55 -0400 Message-Id: <20210502180755.445-2-longman@redhat.com> In-Reply-To: <20210502180755.445-1-longman@redhat.com> References: <20210502180755.445-1-longman@redhat.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The obj_cgroup array (memcg_data) embedded in the page structure is allocated at the first instance an accounted memory allocation happens. With the right size object, it is possible that the allocated obj_cgroup array comes from the same slab that requires memory accounting. If this happens, the slab will never become empty again as there is at least one object left (the obj_cgroup array) in the slab. With instructmentation code added to detect this situation, I got 76 hits on the kmalloc-192 slab when booting up a test kernel on a VM. So this can really happen. To avoid the creation of these unfreeable slabs, a check is added to memcg_alloc_page_obj_cgroups() to detect that and double the size of the array in case it happens to make sure that it comes from a different kmemcache. This change, however, does not completely eliminate the presence of unfreeable slabs which can still happen if a circular obj_cgroup array dependency is formed. Fixes: 286e04b8ed7a ("mm: memcg/slab: allocate obj_cgroups for non-root slab pages") Signed-off-by: Waiman Long --- mm/memcontrol.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index b0695d3aa530..44852ac048c3 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2876,12 +2876,24 @@ int memcg_alloc_page_obj_cgroups(struct page *page, struct kmem_cache *s, */ objects = max(objs_per_slab_page(s, page), (int)(sizeof(struct rcu_head)/sizeof(void *))); - +retry: vec = kcalloc_node(objects, sizeof(struct obj_cgroup *), gfp, page_to_nid(page)); if (!vec) return -ENOMEM; + /* + * The allocated vector should not come from the same slab. + * Otherwise, this slab will never become empty. Double the size + * in this case to make sure that the vector comes from a different + * kmemcache. + */ + if (unlikely(virt_to_head_page(vec) == page)) { + kfree(vec); + objects *= 2; + goto retry; + } + memcg_data = (unsigned long) vec | MEMCG_DATA_OBJCGS; if (new_page) { /* -- 2.18.1