From: Jens Axboe <axboe@kernel.dk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Linux-MM <linux-mm@kvack.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
linux-block <linux-block@vger.kernel.org>,
Matthew Wilcox <willy@infradead.org>, Chris Mason <clm@fb.com>,
Dave Chinner <david@fromorbit.com>,
Johannes Weiner <hannes@cmpxchg.org>
Subject: Re: [PATCHSET v3 0/5] Support for RWF_UNCACHED
Date: Wed, 11 Dec 2019 12:34:40 -0700 [thread overview]
Message-ID: <e43a2700-8625-e136-dc9d-d0d2da5d96ac@kernel.dk> (raw)
In-Reply-To: <d0adcde2-3106-4fea-c047-4d17111bab70@kernel.dk>
On 12/11/19 10:56 AM, Jens Axboe wrote:
>> But I think most of the regular IO call chains come through
>> "mark_page_accessed()". So _that_ is the part you want to avoid (and
>> maybe the workingset code). And that should be fairly straightforward,
>> I think.
>
> Sure, I can give that a go and see how that behaves.
Before doing that, I ran a streamed read test instead of just random
reads, and the behavior is roughly the same. kswapd consumes a bit less
CPU, but it's still very active once the page cache has been filled. For
specifics on the setup, I deliberately boot the box with 32G of RAM, and
the dataset is 320G. My initial tests were with 1 320G file, but
Johannes complained about that so I went to 32 10G files instead. That's
what I'm currently using.
For the random test case, top of profile for kswapd is:
+ 33.49% kswapd0 [kernel.vmlinux] [k] xas_create ◆
+ 7.93% kswapd0 [kernel.vmlinux] [k] __isolate_lru_page ▒
+ 7.18% kswapd0 [kernel.vmlinux] [k] unlock_page ▒
+ 5.90% kswapd0 [kernel.vmlinux] [k] free_pcppages_bulk ▒
+ 5.64% kswapd0 [kernel.vmlinux] [k] _raw_spin_lock_irqsave ▒
+ 5.57% kswapd0 [kernel.vmlinux] [k] shrink_page_list ▒
+ 3.48% kswapd0 [kernel.vmlinux] [k] __remove_mapping ▒
+ 3.35% kswapd0 [kernel.vmlinux] [k] isolate_lru_pages ▒
+ 3.14% kswapd0 [kernel.vmlinux] [k] __delete_from_page_cache ▒
Next I ran with NOT calling mark_page_accessed() to see if that makes a
difference. See patch below, I just applied this on top of this patchset
and added a new RWF_NOACCESS flag for it for ease of teting. I verified
that we are indeed skipping the mark_page_accessed() call in
generic_file_buffered_read().
I can't tell a difference in the results, there's no discernable
difference between NOT calling mark_page_accessed() or calling it.
Behavior seems about the same, in terms of pre and post page cache full,
and kswapd still churns a lot once the page cache is filled up.
--
Jens Axboe
next prev parent reply other threads:[~2019-12-11 19:34 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-11 15:29 [PATCHSET v3 0/5] Support for RWF_UNCACHED Jens Axboe
2019-12-11 15:29 ` [PATCH 1/5] fs: add read support " Jens Axboe
2019-12-11 15:29 ` [PATCH 2/5] mm: make generic_perform_write() take a struct kiocb Jens Axboe
2019-12-11 15:29 ` [PATCH 3/5] mm: make buffered writes work with RWF_UNCACHED Jens Axboe
2019-12-11 15:29 ` [PATCH 4/5] iomap: pass in the write_begin/write_end flags to iomap_actor Jens Axboe
2019-12-11 17:19 ` Linus Torvalds
2019-12-11 15:29 ` [PATCH 5/5] iomap: support RWF_UNCACHED for buffered writes Jens Axboe
2019-12-11 17:19 ` Matthew Wilcox
2019-12-11 18:05 ` Jens Axboe
2019-12-12 22:34 ` Dave Chinner
2019-12-13 0:54 ` Jens Axboe
2019-12-13 0:57 ` Jens Axboe
2019-12-16 4:17 ` Dave Chinner
2019-12-17 14:31 ` Jens Axboe
2019-12-18 0:49 ` Dave Chinner
2019-12-18 1:01 ` Jens Axboe
2019-12-11 17:37 ` [PATCHSET v3 0/5] Support for RWF_UNCACHED Linus Torvalds
2019-12-11 17:56 ` Jens Axboe
2019-12-11 19:14 ` Linus Torvalds
2019-12-11 19:34 ` Jens Axboe [this message]
2019-12-11 20:03 ` Linus Torvalds
2019-12-11 20:08 ` Jens Axboe
2019-12-11 20:18 ` Linus Torvalds
2019-12-11 21:04 ` Johannes Weiner
2019-12-12 1:30 ` Jens Axboe
2019-12-11 23:41 ` Jens Axboe
2019-12-12 1:08 ` Linus Torvalds
2019-12-12 1:11 ` Jens Axboe
2019-12-12 1:22 ` Linus Torvalds
2019-12-12 1:29 ` Jens Axboe
2019-12-12 1:41 ` Linus Torvalds
2019-12-12 1:56 ` Matthew Wilcox
2019-12-12 2:47 ` Linus Torvalds
2019-12-12 17:52 ` Matthew Wilcox
2019-12-12 18:29 ` Linus Torvalds
2019-12-12 20:05 ` Matthew Wilcox
2019-12-12 1:41 ` Jens Axboe
2019-12-12 1:49 ` Linus Torvalds
2019-12-12 1:09 ` Jens Axboe
2019-12-12 2:03 ` Jens Axboe
2019-12-12 2:10 ` Jens Axboe
2019-12-12 2:21 ` Matthew Wilcox
2019-12-12 2:38 ` Jens Axboe
2019-12-12 22:18 ` Dave Chinner
2019-12-13 1:32 ` Chris Mason
2020-01-07 17:42 ` Christoph Hellwig
2020-01-08 14:09 ` Chris Mason
2020-02-01 10:33 ` Andres Freund
2019-12-11 20:43 ` Matthew Wilcox
2019-12-11 20:04 ` Jens Axboe
2019-12-12 10:44 ` Martin Steigerwald
2019-12-12 15:16 ` Jens Axboe
2019-12-12 21:45 ` Martin Steigerwald
2019-12-12 22:15 ` Jens Axboe
2019-12-12 22:18 ` Linus Torvalds
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