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From: Goldwyn Rodrigues <rgoldwyn@suse.de>
To: linux-fsdevel@vger.kernel.org
Cc: jack@suse.com, hch@infradead.org, linux-block@vger.kernel.org,
	linux-btrfs@vger.kernel.org, linux-ext4@vger.kernel.org,
	linux-xfs@vger.kernel.org, sagi@grimberg.me, avi@scylladb.com,
	axboe@kernel.dk, linux-api@vger.kernel.org, willy@infradead.org,
	tom.leiming@gmail.com, Goldwyn Rodrigues <rgoldwyn@suse.com>
Subject: [PATCH 3/8] nowait aio: return if direct write will trigger writeback
Date: Mon,  3 Apr 2017 13:53:02 -0500	[thread overview]
Message-ID: <20170403185307.6243-4-rgoldwyn@suse.de> (raw)
In-Reply-To: <20170403185307.6243-1-rgoldwyn@suse.de>

From: Goldwyn Rodrigues <rgoldwyn@suse.com>

Find out if the write will trigger a wait due to writeback. If yes,
return -EAGAIN.

This introduces a new function filemap_range_has_page() which
returns true if the file's mapping has a page within the range
mentioned.

Return -EINVAL for buffered AIO: there are multiple causes of
delay such as page locks, dirty throttling logic, page loading
from disk etc. which cannot be taken care of.
---
 include/linux/fs.h |  2 ++
 mm/filemap.c       | 50 +++++++++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 49 insertions(+), 3 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 802cfe2..4721136 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2515,6 +2515,8 @@ extern int filemap_fdatawait(struct address_space *);
 extern void filemap_fdatawait_keep_errors(struct address_space *);
 extern int filemap_fdatawait_range(struct address_space *, loff_t lstart,
 				   loff_t lend);
+extern int filemap_range_has_page(struct address_space *, loff_t lstart,
+				   loff_t lend);
 extern int filemap_write_and_wait(struct address_space *mapping);
 extern int filemap_write_and_wait_range(struct address_space *mapping,
 				        loff_t lstart, loff_t lend);
diff --git a/mm/filemap.c b/mm/filemap.c
index e08f3b9..c020e23 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -376,6 +376,39 @@ int filemap_flush(struct address_space *mapping)
 }
 EXPORT_SYMBOL(filemap_flush);
 
+/**
+ * filemap_range_has_page - check if a page exists in range.
+ * @mapping:		address space structure to wait for
+ * @start_byte:		offset in bytes where the range starts
+ * @end_byte:		offset in bytes where the range ends (inclusive)
+ *
+ * Find at least one page in the range supplied, usually used to check if
+ * direct writing in this range will trigger a writeback.
+ */
+int filemap_range_has_page(struct address_space *mapping,
+				loff_t start_byte, loff_t end_byte)
+{
+	pgoff_t index = start_byte >> PAGE_SHIFT;
+	pgoff_t end = end_byte >> PAGE_SHIFT;
+	struct pagevec pvec;
+	int ret;
+
+	if (end_byte < start_byte)
+		return 0;
+
+	if (mapping->nrpages == 0)
+		return 0;
+
+	pagevec_init(&pvec, 0);
+	ret = pagevec_lookup(&pvec, mapping, index, 1);
+	if (!ret)
+		return 0;
+	ret = (pvec.pages[0]->index <= end);
+	pagevec_release(&pvec);
+	return ret;
+}
+EXPORT_SYMBOL(filemap_range_has_page);
+
 static int __filemap_fdatawait_range(struct address_space *mapping,
 				     loff_t start_byte, loff_t end_byte)
 {
@@ -2640,6 +2673,9 @@ inline ssize_t generic_write_checks(struct kiocb *iocb, struct iov_iter *from)
 
 	pos = iocb->ki_pos;
 
+	if ((iocb->ki_flags & IOCB_NOWAIT) && !(iocb->ki_flags & IOCB_DIRECT))
+		return -EINVAL;
+
 	if (limit != RLIM_INFINITY) {
 		if (iocb->ki_pos >= limit) {
 			send_sig(SIGXFSZ, current, 0);
@@ -2709,9 +2745,17 @@ generic_file_direct_write(struct kiocb *iocb, struct iov_iter *from)
 	write_len = iov_iter_count(from);
 	end = (pos + write_len - 1) >> PAGE_SHIFT;
 
-	written = filemap_write_and_wait_range(mapping, pos, pos + write_len - 1);
-	if (written)
-		goto out;
+	if (iocb->ki_flags & IOCB_NOWAIT) {
+		/* If there are pages to writeback, return */
+		if (filemap_range_has_page(inode->i_mapping, pos,
+					   pos + iov_iter_count(from)))
+			return -EAGAIN;
+	} else {
+		written = filemap_write_and_wait_range(mapping, pos,
+							pos + write_len - 1);
+		if (written)
+			goto out;
+	}
 
 	/*
 	 * After a write we want buffered reads to be sure to go to disk to get
-- 
2.10.2


  parent reply	other threads:[~2017-04-03 18:53 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-04-03 18:52 [PATCH 0/8 v4] No wait AIO Goldwyn Rodrigues
     [not found] ` <20170403185307.6243-1-rgoldwyn-l3A5Bk7waGM@public.gmane.org>
2017-04-03 18:53   ` [PATCH 1/8] nowait aio: Introduce IOCB_RW_FLAG_NOWAIT Goldwyn Rodrigues
2017-04-04  6:48     ` Christoph Hellwig
2017-04-03 18:53   ` [PATCH 8/8] nowait aio: btrfs Goldwyn Rodrigues
2017-04-03 18:53 ` [PATCH 2/8] nowait aio: Return if cannot get hold of i_rwsem Goldwyn Rodrigues
2017-04-03 18:53 ` Goldwyn Rodrigues [this message]
2017-04-03 18:53 ` [PATCH 4/8] nowait-aio: Introduce IOMAP_NOWAIT Goldwyn Rodrigues
2017-04-03 18:53 ` [PATCH 5/8] nowait aio: return on congested block device Goldwyn Rodrigues
2017-04-04  6:49   ` Christoph Hellwig
2017-04-03 18:53 ` [PATCH 6/8] nowait aio: ext4 Goldwyn Rodrigues
2017-04-04  7:58   ` Jan Kara
2017-04-04  8:41     ` Christoph Hellwig
2017-04-04 18:41       ` Goldwyn Rodrigues
2017-04-10  7:45         ` Christoph Hellwig
     [not found]           ` <20170410074539.GA18250-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
2017-04-10 12:37             ` Jan Kara
2017-04-10 14:39               ` Christoph Hellwig
2017-04-10 15:13                 ` Jan Kara
2017-04-03 18:53 ` [PATCH 7/8] nowait aio: xfs Goldwyn Rodrigues
2017-04-04  6:52   ` Christoph Hellwig
     [not found]     ` <20170404065211.GD21942-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
2017-04-06 22:54       ` Darrick J. Wong
2017-04-07 11:34         ` Goldwyn Rodrigues
2017-04-07 15:08           ` Darrick J. Wong
  -- strict thread matches above, loose matches on Subject: below --
2017-05-09 12:22 [PATCH 0/8 v7] No wait AIO Goldwyn Rodrigues
2017-05-09 12:22 ` [PATCH 3/8] nowait aio: return if direct write will trigger writeback Goldwyn Rodrigues
2017-05-11  7:42   ` Christoph Hellwig
2017-04-14 12:02 [PATCH 0/8 v6] No wait AIO Goldwyn Rodrigues
2017-04-14 12:02 ` [PATCH 3/8] nowait aio: return if direct write will trigger writeback Goldwyn Rodrigues
2017-03-15 21:50 [PATCH 0/8 v3] No wait AIO Goldwyn Rodrigues
2017-03-15 21:51 ` [PATCH 3/8] nowait aio: return if direct write will trigger writeback Goldwyn Rodrigues
2017-03-16 13:08   ` Matthew Wilcox
2017-03-16 13:46     ` Goldwyn Rodrigues
2017-03-16 13:20   ` Matthew Wilcox
     [not found]     ` <20170316132052.GG4033-PfSpb0PWhxZc2C7mugBRk2EX/6BAtgUQ@public.gmane.org>
2017-03-16 13:46       ` Goldwyn Rodrigues

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