From: Qu Wenruo <wqu@suse.com>
To: linux-btrfs@vger.kernel.org
Subject: [PATCH v3 4/4] btrfs: avoid allocating unnecessary page pointers
Date: Tue, 25 Aug 2020 13:48:08 +0800 [thread overview]
Message-ID: <20200825054808.16241-5-wqu@suse.com> (raw)
In-Reply-To: <20200825054808.16241-1-wqu@suse.com>
Commit 142349f541d0 ("btrfs: lower the dirty balance poll interval")
introduced one limit which is definitely suspicious:
- ensure we always have 8 pages allocated
The 8 lower limit looks pretty strange, this means even we're just
writing 4K, we will allocate page pointers for 8 pages no matter what.
To me, this 8 pages look more like a upper limit.
This 8 pages upper limit looks so incorrect that my eyes alawys correct
it into "min(, 8)" other than "max(, 8)".
This patch will use a fixed size (SZ_64K) other than page numbers to
setup the upper limit.
Also, with comment added to show why we need a upper limit.
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
fs/btrfs/file.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 67d2368a8fa6..de6d1c313042 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1561,7 +1561,14 @@ static int calc_nr_pages(loff_t pos, struct iov_iter *iov)
nr_pages = min(nr_pages, current->nr_dirtied_pause -
current->nr_dirtied);
- nr_pages = max(nr_pages, 8);
+
+ /*
+ * Limit the batch to 64K, too large batch may lead to higher memory
+ * pressure and increase the possibility of short-copy.
+ * With more and more short-copy, the benefit of batch copy would be
+ * hugely reduced, as we will fall back to page-by-page copy.
+ */
+ nr_pages = min(nr_pages, SZ_64K / PAGE_SIZE);
return nr_pages;
}
--
2.28.0
next prev parent reply other threads:[~2020-08-25 5:48 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-25 5:48 [PATCH v3 0/4] btrfs: basic refactor of btrfs_buffered_write() Qu Wenruo
2020-08-25 5:48 ` [PATCH v3 1/4] btrfs: refactor @nrptrs calculation " Qu Wenruo
2020-08-25 5:48 ` [PATCH v3 2/4] btrfs: refactor btrfs_buffered_write() into process_one_batch() Qu Wenruo
2020-08-25 5:48 ` [PATCH v3 3/4] btrfs: remove the again: tag in process_one_batch() Qu Wenruo
2020-08-25 5:48 ` Qu Wenruo [this message]
2020-08-25 7:46 ` [PATCH v3 4/4] btrfs: avoid allocating unnecessary page pointers kernel test robot
2020-08-25 7:57 ` kernel test robot
2020-08-26 12:31 ` kernel test robot
2020-08-25 11:44 ` [PATCH v3 0/4] btrfs: basic refactor of btrfs_buffered_write() Christoph Hellwig
2020-08-25 13:32 ` Goldwyn Rodrigues
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200825054808.16241-5-wqu@suse.com \
--to=wqu@suse.com \
--cc=linux-btrfs@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).