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From: Kent Overstreet <kent.overstreet@gmail.com>
To: Andreas Dilger <adilger@dilger.ca>
Cc: Dave Chinner <david@fromorbit.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Dave Chinner <dchinner@redhat.com>,
	"Darrick J . Wong" <darrick.wong@oracle.com>,
	Christoph Hellwig <hch@lst.de>,
	Matthew Wilcox <willy@infradead.org>,
	Amir Goldstein <amir73il@gmail.com>, Jan Kara <jack@suse.cz>,
	Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
	linux-xfs <linux-xfs@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Josef Bacik <josef@toxicpanda.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: pagecache locking (was: bcachefs status update) merged)
Date: Thu, 13 Jun 2019 17:21:12 -0400	[thread overview]
Message-ID: <20190613212112.GB28171@kmo-pixel> (raw)
In-Reply-To: <AE838C22-1A11-4F93-AB88-80CF009BD301@dilger.ca>

On Thu, Jun 13, 2019 at 03:13:40PM -0600, Andreas Dilger wrote:
> There are definitely workloads that require multiple threads doing non-overlapping
> writes to a single file in HPC.  This is becoming an increasingly common problem
> as the number of cores on a single client increase, since there is typically one
> thread per core trying to write to a shared file.  Using multiple files (one per
> core) is possible, but that has file management issues for users when there are a
> million cores running on the same job/file (obviously not on the same client node)
> dumping data every hour.

Mixed buffered and O_DIRECT though? That profile looks like just buffered IO to
me.

> We were just looking at this exact problem last week, and most of the threads are
> spinning in grab_cache_page_nowait->add_to_page_cache_lru() and set_page_dirty()
> when writing at 1.9GB/s when they could be writing at 5.8GB/s (when threads are
> writing O_DIRECT instead of buffered).  Flame graph is attached for 16-thread case,
> but high-end systems today easily have 2-4x that many cores.

Yeah I've been spending some time on buffered IO performance too - 4k page
overhead is a killer.

bcachefs has a buffered write path that looks up multiple pages at a time and
locks them, and then copies the data to all the pages at once (I stole the idea
from btrfs). It was a very significant performance increase.

https://evilpiepirate.org/git/bcachefs.git/tree/fs/bcachefs/fs-io.c#n1498

  reply	other threads:[~2019-06-13 21:21 UTC|newest]

Thread overview: 62+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-10 19:14 bcachefs status update (it's done cooking; let's get this sucker merged) Kent Overstreet
2019-06-10 19:14 ` [PATCH 01/12] Compiler Attributes: add __flatten Kent Overstreet
2019-06-12 17:16   ` Greg KH
2019-06-10 19:14 ` [PATCH 02/12] locking: SIX locks (shared/intent/exclusive) Kent Overstreet
2019-06-10 19:14 ` [PATCH 03/12] mm: pagecache add lock Kent Overstreet
2019-06-10 19:14 ` [PATCH 04/12] mm: export find_get_pages() Kent Overstreet
2019-06-10 19:14 ` [PATCH 05/12] fs: insert_inode_locked2() Kent Overstreet
2019-06-10 19:14 ` [PATCH 06/12] fs: factor out d_mark_tmpfile() Kent Overstreet
2019-06-10 19:14 ` [PATCH 07/12] Propagate gfp_t when allocating pte entries from __vmalloc Kent Overstreet
2019-06-10 19:14 ` [PATCH 08/12] block: Add some exports for bcachefs Kent Overstreet
2019-06-10 19:14 ` [PATCH 09/12] bcache: optimize continue_at_nobarrier() Kent Overstreet
2019-06-10 19:14 ` [PATCH 10/12] bcache: move closures to lib/ Kent Overstreet
2019-06-11 10:25   ` Coly Li
2019-06-13  7:28   ` Christoph Hellwig
2019-06-13 11:04     ` Kent Overstreet
2019-06-10 19:14 ` [PATCH 11/12] closures: closure_wait_event() Kent Overstreet
2019-06-11 10:25   ` Coly Li
2019-06-12 17:17   ` Greg KH
2019-06-10 19:14 ` [PATCH 12/12] closures: fix a race on wakeup from closure_sync Kent Overstreet
2019-07-16 10:47   ` Coly Li
2019-07-18  7:46     ` Coly Li
2019-07-22 17:22       ` Kent Overstreet
2019-06-10 20:46 ` bcachefs status update (it's done cooking; let's get this sucker merged) Linus Torvalds
2019-06-11  1:17   ` Kent Overstreet
2019-06-11  4:33     ` Dave Chinner
2019-06-12 16:21       ` Kent Overstreet
2019-06-12 23:02         ` Dave Chinner
2019-06-13 18:36           ` pagecache locking (was: bcachefs status update) merged) Kent Overstreet
2019-06-13 21:13             ` Andreas Dilger
2019-06-13 21:21               ` Kent Overstreet [this message]
2019-06-14  0:35                 ` Dave Chinner
2019-06-13 23:55             ` Dave Chinner
2019-06-14  2:30               ` Linus Torvalds
2019-06-14  7:30                 ` Dave Chinner
2019-06-15  1:15                   ` Linus Torvalds
2019-06-14  3:08               ` Linus Torvalds
2019-06-15  4:01                 ` Linus Torvalds
2019-06-17 22:47                   ` Dave Chinner
2019-06-17 23:38                     ` Linus Torvalds
2019-06-18  4:21                       ` Amir Goldstein
2019-06-19 10:38                         ` Jan Kara
2019-06-19 22:37                           ` Dave Chinner
2019-07-03  0:04                             ` pagecache locking Boaz Harrosh
     [not found]                               ` <DM6PR19MB250857CB8A3A1C8279D6F2F3C5FB0@DM6PR19MB2508.namprd19.prod.outlook.com>
2019-07-03  1:25                                 ` Boaz Harrosh
2019-07-05 23:31                               ` Dave Chinner
2019-07-07 15:05                                 ` Boaz Harrosh
2019-07-07 23:55                                   ` Dave Chinner
2019-07-08 13:31                                 ` Jan Kara
2019-07-09 23:47                                   ` Dave Chinner
2019-07-10  8:41                                     ` Jan Kara
2019-06-14 17:08               ` pagecache locking (was: bcachefs status update) merged) Kent Overstreet
2019-06-19  8:21           ` bcachefs status update (it's done cooking; let's get this sucker merged) Jan Kara
2019-07-03  1:04             ` [PATCH] mm: Support madvise_willneed override by Filesystems Boaz Harrosh
2019-07-03 17:21               ` Jan Kara
2019-07-03 18:03                 ` Boaz Harrosh
2019-06-11  4:55     ` bcachefs status update (it's done cooking; let's get this sucker merged) Linus Torvalds
2019-06-11 14:26       ` Matthew Wilcox
2019-06-11  4:10   ` Dave Chinner
2019-06-11  4:39     ` Linus Torvalds
2019-06-11  7:10       ` Dave Chinner
2019-06-12  2:07         ` Linus Torvalds
2019-07-03  5:59 ` Stefan K

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