diff mbox series

[v2] ext4: bio_alloc with __GFP_DIRECT_RECLAIM never fails

Message ID 20191031092315.139267-1-gaoxiang25@huawei.com
State Accepted, archived
Headers show
Series [v2] ext4: bio_alloc with __GFP_DIRECT_RECLAIM never fails | expand

Commit Message

Gao Xiang Oct. 31, 2019, 9:23 a.m. UTC 
Similar to [1] [2], bio_alloc with __GFP_DIRECT_RECLAIM flags
guarantees bio allocation under some given restrictions, as
stated in block/bio.c and fs/direct-io.c So here it's ok to
not check for NULL value from bio_alloc().

[1] https://lore.kernel.org/r/20191030035518.65477-1-gaoxiang25@huawei.com
[2] https://lore.kernel.org/r/20190830162812.GA10694@infradead.org
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Cc: Ritesh Harjani <riteshh@linux.ibm.com>
Cc: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
---

changes since v1:
 - fix commit message and simplify logic as suggested by Ritesh;
 - add short messages ahead of bio_alloc suggested by Ted.

 fs/ext4/page-io.c  | 57 ++++++++++++++++++----------------------------
 fs/ext4/readpage.c |  6 +++--
 2 files changed, 26 insertions(+), 37 deletions(-)

Comments

Chao Yu Oct. 31, 2019, 9:29 a.m. UTC | #1 
On 2019/10/31 17:23, Gao Xiang wrote:
> Similar to [1] [2], bio_alloc with __GFP_DIRECT_RECLAIM flags
> guarantees bio allocation under some given restrictions, as
> stated in block/bio.c and fs/direct-io.c So here it's ok to
> not check for NULL value from bio_alloc().
> 
> [1] https://lore.kernel.org/r/20191030035518.65477-1-gaoxiang25@huawei.com
> [2] https://lore.kernel.org/r/20190830162812.GA10694@infradead.org
> Cc: Theodore Ts'o <tytso@mit.edu>
> Cc: Andreas Dilger <adilger.kernel@dilger.ca>
> Cc: Ritesh Harjani <riteshh@linux.ibm.com>
> Cc: Chao Yu <yuchao0@huawei.com>
> Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>

Reviewed-by: Chao Yu <yuchao0@huawei.com>

Thanks,
Theodore Ts'o Nov. 15, 2019, 3:19 a.m. UTC | #2 
On Thu, Oct 31, 2019 at 05:29:58PM +0800, Chao Yu wrote:
> On 2019/10/31 17:23, Gao Xiang wrote:
> > Similar to [1] [2], bio_alloc with __GFP_DIRECT_RECLAIM flags
> > guarantees bio allocation under some given restrictions, as
> > stated in block/bio.c and fs/direct-io.c So here it's ok to
> > not check for NULL value from bio_alloc().
> > 
> > [1] https://lore.kernel.org/r/20191030035518.65477-1-gaoxiang25@huawei.com
> > [2] https://lore.kernel.org/r/20190830162812.GA10694@infradead.org
> > Cc: Theodore Ts'o <tytso@mit.edu>
> > Cc: Andreas Dilger <adilger.kernel@dilger.ca>
> > Cc: Ritesh Harjani <riteshh@linux.ibm.com>
> > Cc: Chao Yu <yuchao0@huawei.com>
> > Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
> 
> Reviewed-by: Chao Yu <yuchao0@huawei.com>

Thanks, applied.

					- Ted
Gao Xiang Nov. 15, 2019, 3:24 a.m. UTC | #3 
Hi Ted,

On Thu, Nov 14, 2019 at 10:19:53PM -0500, Theodore Y. Ts'o wrote:
> On Thu, Oct 31, 2019 at 05:29:58PM +0800, Chao Yu wrote:
> > On 2019/10/31 17:23, Gao Xiang wrote:
> > > Similar to [1] [2], bio_alloc with __GFP_DIRECT_RECLAIM flags
> > > guarantees bio allocation under some given restrictions, as
> > > stated in block/bio.c and fs/direct-io.c So here it's ok to
> > > not check for NULL value from bio_alloc().
> > > 
> > > [1] https://lore.kernel.org/r/20191030035518.65477-1-gaoxiang25@huawei.com
> > > [2] https://lore.kernel.org/r/20190830162812.GA10694@infradead.org
> > > Cc: Theodore Ts'o <tytso@mit.edu>
> > > Cc: Andreas Dilger <adilger.kernel@dilger.ca>
> > > Cc: Ritesh Harjani <riteshh@linux.ibm.com>
> > > Cc: Chao Yu <yuchao0@huawei.com>
> > > Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
> > 
> > Reviewed-by: Chao Yu <yuchao0@huawei.com>
> 
> Thanks, applied.
> 
> 					- Ted

Thanks for considering this. Have a nice day.

Thanks,
Gao Xiang
diff mbox series

Patch

diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
index 12ceadef32c5..c92504c1b1ca 100644
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -358,14 +358,16 @@  void ext4_io_submit_init(struct ext4_io_submit *io,
 	io->io_end = NULL;
 }
 
-static int io_submit_init_bio(struct ext4_io_submit *io,
-			      struct buffer_head *bh)
+static void io_submit_init_bio(struct ext4_io_submit *io,
+			       struct buffer_head *bh)
 {
 	struct bio *bio;
 
+	/*
+	 * bio_alloc will _always_ be able to allocate a bio if
+	 * __GFP_DIRECT_RECLAIM is set, see comments for bio_alloc_bioset().
+	 */
 	bio = bio_alloc(GFP_NOIO, BIO_MAX_PAGES);
-	if (!bio)
-		return -ENOMEM;
 	bio->bi_iter.bi_sector = bh->b_blocknr * (bh->b_size >> 9);
 	bio_set_dev(bio, bh->b_bdev);
 	bio->bi_end_io = ext4_end_bio;
@@ -373,13 +375,12 @@  static int io_submit_init_bio(struct ext4_io_submit *io,
 	io->io_bio = bio;
 	io->io_next_block = bh->b_blocknr;
 	wbc_init_bio(io->io_wbc, bio);
-	return 0;
 }
 
-static int io_submit_add_bh(struct ext4_io_submit *io,
-			    struct inode *inode,
-			    struct page *page,
-			    struct buffer_head *bh)
+static void io_submit_add_bh(struct ext4_io_submit *io,
+			     struct inode *inode,
+			     struct page *page,
+			     struct buffer_head *bh)
 {
 	int ret;
 
@@ -388,9 +389,7 @@  static int io_submit_add_bh(struct ext4_io_submit *io,
 		ext4_io_submit(io);
 	}
 	if (io->io_bio == NULL) {
-		ret = io_submit_init_bio(io, bh);
-		if (ret)
-			return ret;
+		io_submit_init_bio(io, bh);
 		io->io_bio->bi_write_hint = inode->i_write_hint;
 	}
 	ret = bio_add_page(io->io_bio, page, bh->b_size, bh_offset(bh));
@@ -398,7 +397,6 @@  static int io_submit_add_bh(struct ext4_io_submit *io,
 		goto submit_and_retry;
 	wbc_account_cgroup_owner(io->io_wbc, page, bh->b_size);
 	io->io_next_block++;
-	return 0;
 }
 
 int ext4_bio_write_page(struct ext4_io_submit *io,
@@ -491,8 +489,14 @@  int ext4_bio_write_page(struct ext4_io_submit *io,
 				gfp_flags |= __GFP_NOFAIL;
 				goto retry_encrypt;
 			}
-			bounce_page = NULL;
-			goto out;
+
+			printk_ratelimited(KERN_ERR "%s: ret = %d\n", __func__, ret);
+			redirty_page_for_writepage(wbc, page);
+			do {
+				clear_buffer_async_write(bh);
+				bh = bh->b_this_page;
+			} while (bh != head);
+			goto unlock;
 		}
 	}
 
@@ -500,30 +504,13 @@  int ext4_bio_write_page(struct ext4_io_submit *io,
 	do {
 		if (!buffer_async_write(bh))
 			continue;
-		ret = io_submit_add_bh(io, inode, bounce_page ?: page, bh);
-		if (ret) {
-			/*
-			 * We only get here on ENOMEM.  Not much else
-			 * we can do but mark the page as dirty, and
-			 * better luck next time.
-			 */
-			break;
-		}
+		io_submit_add_bh(io, inode,
+				 bounce_page ? bounce_page : page, bh);
 		nr_submitted++;
 		clear_buffer_dirty(bh);
 	} while ((bh = bh->b_this_page) != head);
 
-	/* Error stopped previous loop? Clean up buffers... */
-	if (ret) {
-	out:
-		fscrypt_free_bounce_page(bounce_page);
-		printk_ratelimited(KERN_ERR "%s: ret = %d\n", __func__, ret);
-		redirty_page_for_writepage(wbc, page);
-		do {
-			clear_buffer_async_write(bh);
-			bh = bh->b_this_page;
-		} while (bh != head);
-	}
+unlock:
 	unlock_page(page);
 	/* Nothing submitted - we have to end page writeback */
 	if (!nr_submitted)
diff --git a/fs/ext4/readpage.c b/fs/ext4/readpage.c
index a30b203fa461..fef7755300c3 100644
--- a/fs/ext4/readpage.c
+++ b/fs/ext4/readpage.c
@@ -360,10 +360,12 @@  int ext4_mpage_readpages(struct address_space *mapping,
 		if (bio == NULL) {
 			struct bio_post_read_ctx *ctx;
 
+			/*
+			 * bio_alloc will _always_ be able to allocate a bio if
+			 * __GFP_DIRECT_RECLAIM is set, see bio_alloc_bioset().
+			 */
 			bio = bio_alloc(GFP_KERNEL,
 				min_t(int, nr_pages, BIO_MAX_PAGES));
-			if (!bio)
-				goto set_error_page;
 			ctx = get_bio_post_read_ctx(inode, bio, page->index);
 			if (IS_ERR(ctx)) {
 				bio_put(bio);