From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx157.postini.com [74.125.245.157]) by kanga.kvack.org (Postfix) with SMTP id BE1F76B005A for ; Sat, 7 Jan 2012 03:28:37 -0500 (EST) Received: by qcsd17 with SMTP id d17so1540289qcs.14 for ; Sat, 07 Jan 2012 00:28:36 -0800 (PST) Message-ID: <4F08022C.1020208@gmail.com> Date: Sat, 07 Jan 2012 03:28:28 -0500 From: KOSAKI Motohiro MIME-Version: 1.0 Subject: Re: [PATCH 1/2] SHM_UNLOCK: fix long unpreemptible section References: In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Hugh Dickins Cc: Andrew Morton , Minchan Kim , Rik van Riel , Shaohua Li , Eric Dumazet , Johannes Weiner , Michel Lespinasse , linux-kernel@vger.kernel.org, linux-mm@kvack.org (1/6/12 4:10 PM), Hugh Dickins wrote: > scan_mapping_unevictable_pages() is used to make SysV SHM_LOCKed pages > evictable again once the shared memory is unlocked. It does this with > pagevec_lookup()s across the whole object (which might occupy most of > memory), and takes 300ms to unlock 7GB here. A cond_resched() every > PAGEVEC_SIZE pages would be good. > > However, KOSAKI-san points out that this is called under shmem.c's > info->lock, and it's also under shm.c's shm_lock(), both spinlocks. > There is no strong reason for that: we need to take these pages off > the unevictable list soonish, but those locks are not required for it. > > So move the call to scan_mapping_unevictable_pages() from shmem.c's > unlock handling up to shm.c's unlock handling. Remove the recently > added barrier, not needed now we have spin_unlock() before the scan. > > Use get_file(), with subsequent fput(), to make sure we have a > reference to mapping throughout scan_mapping_unevictable_pages(): > that's something that was previously guaranteed by the shm_lock(). > > Remove shmctl's lru_add_drain_all(): we don't fault in pages at > SHM_LOCK time, and we lazily discover them to be Unevictable later, > so it serves no purpose for SHM_LOCK; and serves no purpose for > SHM_UNLOCK, since pages still on pagevec are not marked Unevictable. > > The original code avoided redundant rescans by checking VM_LOCKED > flag at its level: now avoid them by checking shp's SHM_LOCKED. > > The original code called scan_mapping_unevictable_pages() on a > locked area at shm_destroy() time: perhaps we once had accounting > cross-checks which required that, but not now, so skip the overhead > and just let inode eviction deal with them. > > Put check_move_unevictable_page() and scan_mapping_unevictable_pages() > under CONFIG_SHMEM (with stub for the TINY case when ramfs is used), > more as comment than to save space; comment them used for SHM_UNLOCK. > > Signed-off-by: Hugh Dickins > Cc: stable@vger.kernel.org [back to 2.6.32 but will need respins] Looks completely make sense. Reviewed-by: KOSAKI Motohiro -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org