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[195.135.220.15]) by mx.google.com with ESMTPS id x200si2269471wme.45.2017.01.18.04.46.00 for (version=TLS1 cipher=AES128-SHA bits=128/128); Wed, 18 Jan 2017 04:46:00 -0800 (PST) Date: Wed, 18 Jan 2017 13:45:55 +0100 From: Michal Hocko Subject: Re: [Update][PATCH v5 7/9] mm/swap: Add cache for swap slots allocation Message-ID: <20170118124555.GQ7015@dhcp22.suse.cz> References: <35de301a4eaa8daa2977de6e987f2c154385eb66.1484082593.git.tim.c.chen@linux.intel.com> <87tw8ymm2z.fsf_-_@yhuang-dev.intel.com> <20170117214234.GA14383@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170117214234.GA14383@linux.intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: Tim Chen Cc: "Huang, Ying" , Andrew Morton , dave.hansen@intel.com, ak@linux.intel.com, aaron.lu@intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hugh Dickins , Shaohua Li , Minchan Kim , Rik van Riel , Andrea Arcangeli , "Kirill A . Shutemov" , Vladimir Davydov , Johannes Weiner , Hillf Danton , Christian Borntraeger , Jonathan Corbet , Tim C Chen On Tue 17-01-17 13:42:35, Tim Chen wrote: [...] > Date: Tue, 17 Jan 2017 12:57:00 -0800 > Subject: [PATCH] mm/swap: Use raw_cpu_ptr over this_cpu_ptr for swap slots > access > To: Andrew Morton > Cc: Ying Huang , dave.hansen@intel.com, ak@linux.intel.com, aaron.lu@intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hugh Dickins , Shaohua Li , Minchan Kim , Rik van Riel , Andrea Arcangeli , Kirill A . Shutemov , Vladimir Davydov , Johannes Weiner , Michal Hocko , Hillf Danton , Christian Borntraeger , Jonathan Corbet > > From: "Huang, Ying" > > The usage of this_cpu_ptr in get_swap_page causes a bug warning > as it is used in pre-emptible code. > > [ 57.812314] BUG: using smp_processor_id() in preemptible [00000000] code: kswapd0/527 > [ 57.814360] caller is debug_smp_processor_id+0x17/0x19 > [ 57.815237] CPU: 1 PID: 527 Comm: kswapd0 Tainted: G W 4.9.0-mmotm-00135-g4e9a9895ebef #1042 > [ 57.816019] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.1-1 04/01/2014 > [ 57.816019] ffffc900001939c0 ffffffff81329c60 0000000000000001 ffffffff81a0ce06 > [ 57.816019] ffffc900001939f0 ffffffff81343c2a 00000000000137a0 ffffea0000dfd2a0 > [ 57.816019] ffff88003c49a700 ffffc90000193b10 ffffc90000193a00 ffffffff81343c53 > [ 57.816019] Call Trace: > [ 57.816019] [] dump_stack+0x68/0x92 > [ 57.816019] [] check_preemption_disabled+0xce/0xe0 > [ 57.816019] [] debug_smp_processor_id+0x17/0x19 > [ 57.816019] [] get_swap_page+0x19/0x183 > [ 57.816019] [] shmem_writepage+0xce/0x38c > [ 57.816019] [] shrink_page_list+0x81f/0xdbf > [ 57.816019] [] shrink_inactive_list+0x2ab/0x594 > [ 57.816019] [] shrink_node_memcg+0x4c7/0x673 > [ 57.816019] [] shrink_node+0xc4/0x282 > [ 57.816019] [] ? shrink_node+0xc4/0x282 > [ 57.816019] [] kswapd+0x656/0x834 > > Logic wise, We do allow pre-emption as per cpu ptr cache->slots is > protected by the mutex cache->alloc_lock. We switch the > inappropriately used this_cpu_ptr to raw_cpu_ptr for per cpu ptr > access of cache->slots. OK, that looks better. I would still appreciate something like the following folded in diff --git a/include/linux/swap_slots.h b/include/linux/swap_slots.h index fb907346c5c6..0afe748453a7 100644 --- a/include/linux/swap_slots.h +++ b/include/linux/swap_slots.h @@ -11,6 +11,7 @@ struct swap_slots_cache { bool lock_initialized; + /* protects slots, nr, cur */ struct mutex alloc_lock; swp_entry_t *slots; int nr; > > Reported-by: Michal Hocko > Signed-off-by: "Huang, Ying" > Signed-off-by: Tim Chen Reviewed-by: Michal Hocko Thanks! > --- > mm/swap_slots.c | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-) > > diff --git a/mm/swap_slots.c b/mm/swap_slots.c > index 8cf941e..9b5bc86 100644 > --- a/mm/swap_slots.c > +++ b/mm/swap_slots.c > @@ -303,7 +303,16 @@ swp_entry_t get_swap_page(void) > swp_entry_t entry, *pentry; > struct swap_slots_cache *cache; > > - cache = this_cpu_ptr(&swp_slots); > + /* > + * Preemption is allowed here, because we may sleep > + * in refill_swap_slots_cache(). But it is safe, because > + * accesses to the per-CPU data structure are protected by the > + * mutex cache->alloc_lock. > + * > + * The alloc path here does not touch cache->slots_ret > + * so cache->free_lock is not taken. > + */ > + cache = raw_cpu_ptr(&swp_slots); > > entry.val = 0; > if (check_cache_active()) { > -- > 2.5.5 > -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org