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[195.135.220.15]) by mx.google.com with ESMTPS id f10si1179364edf.247.2019.03.27.11.17.03 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 27 Mar 2019 11:17:03 -0700 (PDT) Received-SPF: softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) smtp.mailfrom=mhocko@kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org 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 9ED1AAD73; Wed, 27 Mar 2019 18:17:02 +0000 (UTC) Date: Wed, 27 Mar 2019 19:17:00 +0100 From: Michal Hocko To: Catalin Marinas Cc: Qian Cai , akpm@linux-foundation.org, cl@linux.com, willy@infradead.org, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4] kmemleak: survive in a low-memory situation Message-ID: <20190327181700.GO11927@dhcp22.suse.cz> References: <20190327005948.24263-1-cai@lca.pw> <20190327084432.GA11927@dhcp22.suse.cz> <20190327172955.GB17247@arrakis.emea.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190327172955.GB17247@arrakis.emea.arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) 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: On Wed 27-03-19 17:29:57, Catalin Marinas wrote: [...] > Quick attempt below and it needs some more testing (pretty random pick > of the EMERGENCY_POOL_SIZE value). Also, with __GFP_NOFAIL removed, are > the other flags safe or we should trim them further? I would be still careful about __GFP_NORETRY. I pressume that the primary purpose is to prevent from the OOM killer but this makes the allocation failure much more likely. So if anything __GFP_RETRY_MAYFAIL would suite better for that purpose. But I am not really sure that this is worth bothering. > ---------------8<------------------------------- > >From dc4194539f8191bb754901cea74c86e7960886f8 Mon Sep 17 00:00:00 2001 > From: Catalin Marinas > Date: Wed, 27 Mar 2019 17:20:57 +0000 > Subject: [PATCH] mm: kmemleak: Add an emergency allocation pool for kmemleak > objects > > This patch adds an emergency pool for struct kmemleak_object in case the > normal kmem_cache_alloc() fails under the gfp constraints passed by the > slab allocation caller. The patch also removes __GFP_NOFAIL which does > not play well with other gfp flags (introduced by commit d9570ee3bd1d, > "kmemleak: allow to coexist with fault injection"). Thank you! This is definitely a step into the right direction. Maybe the pool allocation logic will need some tuning - e.g. does it make sense to allocate into the pool from sleepable allocations - or is it sufficient to refill on free. Something for the real workloads to tell, I guess. > Suggested-by: Michal Hocko > Signed-off-by: Catalin Marinas > --- > mm/kmemleak.c | 59 +++++++++++++++++++++++++++++++++++++++++++++++++-- > 1 file changed, 57 insertions(+), 2 deletions(-) > > diff --git a/mm/kmemleak.c b/mm/kmemleak.c > index 6c318f5ac234..366a680cff7c 100644 > --- a/mm/kmemleak.c > +++ b/mm/kmemleak.c > @@ -127,7 +127,7 @@ > /* GFP bitmask for kmemleak internal allocations */ > #define gfp_kmemleak_mask(gfp) (((gfp) & (GFP_KERNEL | GFP_ATOMIC)) | \ > __GFP_NORETRY | __GFP_NOMEMALLOC | \ > - __GFP_NOWARN | __GFP_NOFAIL) > + __GFP_NOWARN) > > /* scanning area inside a memory block */ > struct kmemleak_scan_area { > @@ -191,11 +191,16 @@ struct kmemleak_object { > #define HEX_ASCII 1 > /* max number of lines to be printed */ > #define HEX_MAX_LINES 2 > +/* minimum emergency pool size */ > +#define EMERGENCY_POOL_SIZE (NR_CPUS * 4) > > /* the list of all allocated objects */ > static LIST_HEAD(object_list); > /* the list of gray-colored objects (see color_gray comment below) */ > static LIST_HEAD(gray_list); > +/* emergency pool allocation */ > +static LIST_HEAD(emergency_list); > +static int emergency_pool_size; > /* search tree for object boundaries */ > static struct rb_root object_tree_root = RB_ROOT; > /* rw_lock protecting the access to object_list and object_tree_root */ > @@ -467,6 +472,43 @@ static int get_object(struct kmemleak_object *object) > return atomic_inc_not_zero(&object->use_count); > } > > +/* > + * Emergency pool allocation and freeing. kmemleak_lock must not be held. > + */ > +static struct kmemleak_object *emergency_alloc(void) > +{ > + unsigned long flags; > + struct kmemleak_object *object; > + > + write_lock_irqsave(&kmemleak_lock, flags); > + object = list_first_entry_or_null(&emergency_list, typeof(*object), object_list); > + if (object) { > + list_del(&object->object_list); > + emergency_pool_size--; > + } > + write_unlock_irqrestore(&kmemleak_lock, flags); > + > + return object; > +} > + > +/* > + * Return true if object added to the emergency pool, false otherwise. > + */ > +static bool emergency_free(struct kmemleak_object *object) > +{ > + unsigned long flags; > + > + if (emergency_pool_size >= EMERGENCY_POOL_SIZE) > + return false; > + > + write_lock_irqsave(&kmemleak_lock, flags); > + list_add(&object->object_list, &emergency_list); > + emergency_pool_size++; > + write_unlock_irqrestore(&kmemleak_lock, flags); > + > + return true; > +} > + > /* > * RCU callback to free a kmemleak_object. > */ > @@ -485,7 +527,8 @@ static void free_object_rcu(struct rcu_head *rcu) > hlist_del(&area->node); > kmem_cache_free(scan_area_cache, area); > } > - kmem_cache_free(object_cache, object); > + if (!emergency_free(object)) > + kmem_cache_free(object_cache, object); > } > > /* > @@ -577,6 +620,8 @@ static struct kmemleak_object *create_object(unsigned long ptr, size_t size, > unsigned long untagged_ptr; > > object = kmem_cache_alloc(object_cache, gfp_kmemleak_mask(gfp)); > + if (!object) > + object = emergency_alloc(); > if (!object) { > pr_warn("Cannot allocate a kmemleak_object structure\n"); > kmemleak_disable(); > @@ -2127,6 +2172,16 @@ void __init kmemleak_init(void) > kmemleak_warning = 0; > } > } > + > + /* populate the emergency allocation pool */ > + while (emergency_pool_size < EMERGENCY_POOL_SIZE) { > + struct kmemleak_object *object; > + > + object = kmem_cache_alloc(object_cache, GFP_KERNEL); > + if (!object) > + break; > + emergency_free(object); > + } > } > > /* -- Michal Hocko SUSE Labs