io-uring.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Jens Axboe <axboe@kernel.dk>
To: io-uring@vger.kernel.org
Cc: Jens Axboe <axboe@kernel.dk>,
	Matthew Wilcox <willy@infradead.org>,
	Johannes Weiner <hannes@cmpxchg.org>
Subject: [PATCH 02/18] readahead: use limited read-ahead to satisfy read
Date: Fri, 16 Oct 2020 10:02:08 -0600	[thread overview]
Message-ID: <20201016160224.1575329-3-axboe@kernel.dk> (raw)
In-Reply-To: <20201016160224.1575329-1-axboe@kernel.dk>

Willy reports that there's a case where async buffered reads will be
blocking, and that's due to not using read-ahead to generate the reads
when read-ahead is disabled. io_uring relies on read-ahead triggering
the reads, if not, it needs to fallback to threaded helpers.

For the case where read-ahead is disabled on the file, or if the cgroup
is congested, ensure that we can at least do 1 page of read-ahead to
make progress on the read in an async fashion. This could potentially be
larger, but it's not needed in terms of functionality, so let's error on
the side of caution as larger counts of pages may run into reclaim
issues (particularly if we're congested).

Reported-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 mm/readahead.c | 22 +++++++++++++++-------
 1 file changed, 15 insertions(+), 7 deletions(-)

diff --git a/mm/readahead.c b/mm/readahead.c
index 3c9a8dd7c56c..b014d122e656 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -568,15 +568,23 @@ void page_cache_sync_readahead(struct address_space *mapping,
 			       struct file_ra_state *ra, struct file *filp,
 			       pgoff_t index, unsigned long req_count)
 {
-	/* no read-ahead */
-	if (!ra->ra_pages)
-		return;
+	bool do_forced_ra = filp && (filp->f_mode & FMODE_RANDOM);
 
-	if (blk_cgroup_congested())
-		return;
+	/*
+	 * Even if read-ahead is disabled, start this request as read-ahead.
+	 * This makes regular read-ahead disabled use the same path as normal
+	 * reads, instead of having to punt to ->readpage() manually. We limit
+	 * ourselves to 1 page for this case, to avoid causing problems if
+	 * we're congested or tight on memory.
+	 */
+	if (!ra->ra_pages || blk_cgroup_congested()) {
+		if (!filp)
+			return;
+		req_count = 1;
+		do_forced_ra = true;
+	}
 
-	/* be dumb */
-	if (filp && (filp->f_mode & FMODE_RANDOM)) {
+	if (do_forced_ra) {
 		force_page_cache_readahead(mapping, filp, index, req_count);
 		return;
 	}
-- 
2.28.0


  parent reply	other threads:[~2020-10-16 16:02 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-16 16:02 [PATCHES 0/10] Fixes queued up for 5.10 Jens Axboe
2020-10-16 16:02 ` [PATCH 01/18] io_uring: Fix sizeof() mismatch Jens Axboe
2020-10-16 16:02 ` Jens Axboe [this message]
2020-10-16 16:02 ` [PATCH 03/18] io_uring: don't clear IOCB_NOWAIT for async buffered retry Jens Axboe
2020-10-16 16:02 ` [PATCH 04/18] io_uring: don't set COMP_LOCKED if won't put Jens Axboe
2020-10-16 16:02 ` [PATCH 05/18] io_uring: don't unnecessarily clear F_LINK_TIMEOUT Jens Axboe
2020-10-16 16:02 ` [PATCH 06/18] io_uring: don't put a poll req under spinlock Jens Axboe
2020-10-16 16:02 ` [PATCH 07/18] io_uring: dig out COMP_LOCK from deep call chain Jens Axboe
2020-10-16 16:02 ` [PATCH 08/18] io_uring: fix REQ_F_COMP_LOCKED by killing it Jens Axboe
2020-10-16 16:02 ` [PATCH 09/18] Revert "io_uring: mark io_uring_fops/io_op_defs as __read_mostly" Jens Axboe
2020-10-16 16:02 ` [PATCH 10/18] io_uring: fix error path cleanup in io_sqe_files_register() Jens Axboe
2020-10-16 16:02 ` [PATCH 11/18] io-wq: assign NUMA node locality if appropriate Jens Axboe
2020-10-16 16:02 ` [PATCH 12/18] io_uring: pass required context in as flags Jens Axboe
2020-10-16 16:02 ` [PATCH 13/18] io_uring: rely solely on work flags to determine personality Jens Axboe
2020-10-16 16:02 ` [PATCH 14/18] io_uring: move io identity items into separate struct Jens Axboe
2020-10-16 16:02 ` [PATCH 15/18] io_uring: COW io_identity on mismatch Jens Axboe
2020-10-16 16:02 ` [PATCH 16/18] io_uring: store io_identity in io_uring_task Jens Axboe
2020-10-16 16:02 ` [PATCH 17/18] io_uring: assign new io_identity for task if members have changed Jens Axboe
2020-10-16 16:02 ` [PATCH 18/18] io_uring: use percpu counters to track inflight requests Jens Axboe

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=20201016160224.1575329-3-axboe@kernel.dk \
    --to=axboe@kernel.dk \
    --cc=hannes@cmpxchg.org \
    --cc=io-uring@vger.kernel.org \
    --cc=willy@infradead.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).