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From: Qu Wenruo <wqu@suse.com>
To: linux-btrfs@vger.kernel.org
Subject: [PATCH 03/27] btrfs: use async_chunk::async_cow to replace the confusing pending pointer
Date: Tue, 13 Jul 2021 14:14:52 +0800	[thread overview]
Message-ID: <20210713061516.163318-4-wqu@suse.com> (raw)
In-Reply-To: <20210713061516.163318-1-wqu@suse.com>

For structure async_chunk, we use a very strange member layout to grab
structure async_cow who owns this async_chunk.

At initialization, it goes like this:

		async_chunk[i].pending = &ctx->num_chunks;

Then at async_cow_free() we do a super weird freeing:

	/*
	 * Since the pointer to 'pending' is at the beginning of the array of
	 * async_chunk's, freeing it ensures the whole array has been freed.
	 */
	if (atomic_dec_and_test(async_chunk->pending))
		kvfree(async_chunk->pending);

This is absolutely an abuse of kvfree().

Replace async_chunk::pending with async_chunk::async_cow, so that we can
grab the async_cow structure directly, without this strange dancing.

And with this change, there is no requirement for any specific member
location.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/inode.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index c8f4d1f8cc82..e5703160718c 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -454,11 +454,10 @@ struct async_chunk {
 	struct list_head extents;
 	struct cgroup_subsys_state *blkcg_css;
 	struct btrfs_work work;
-	atomic_t *pending;
+	struct async_cow *async_cow;
 };
 
 struct async_cow {
-	/* Number of chunks in flight; must be first in the structure */
 	atomic_t num_chunks;
 	struct async_chunk chunks[];
 };
@@ -1324,18 +1323,17 @@ static noinline void async_cow_submit(struct btrfs_work *work)
 static noinline void async_cow_free(struct btrfs_work *work)
 {
 	struct async_chunk *async_chunk;
+	struct async_cow *async_cow;
 
 	async_chunk = container_of(work, struct async_chunk, work);
 	if (async_chunk->inode)
 		btrfs_add_delayed_iput(async_chunk->inode);
 	if (async_chunk->blkcg_css)
 		css_put(async_chunk->blkcg_css);
-	/*
-	 * Since the pointer to 'pending' is at the beginning of the array of
-	 * async_chunk's, freeing it ensures the whole array has been freed.
-	 */
-	if (atomic_dec_and_test(async_chunk->pending))
-		kvfree(async_chunk->pending);
+
+	async_cow = async_chunk->async_cow;
+	if (atomic_dec_and_test(&async_cow->num_chunks))
+		kvfree(async_cow);
 }
 
 static int cow_file_range_async(struct btrfs_inode *inode,
@@ -1396,7 +1394,7 @@ static int cow_file_range_async(struct btrfs_inode *inode,
 		 * lightweight reference for the callback lifetime
 		 */
 		ihold(&inode->vfs_inode);
-		async_chunk[i].pending = &ctx->num_chunks;
+		async_chunk[i].async_cow = ctx;
 		async_chunk[i].inode = &inode->vfs_inode;
 		async_chunk[i].start = start;
 		async_chunk[i].end = cur_end;
-- 
2.32.0


  parent reply	other threads:[~2021-07-13  6:15 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-13  6:14 [PATCH 00/27] btrfs: limited subpage compressed write support Qu Wenruo
2021-07-13  6:14 ` [PATCH 01/27] btrfs: remove unused parameter @nr_pages in add_ra_bio_pages() Qu Wenruo
2021-07-13  6:14 ` [PATCH 02/27] btrfs: remove unnecessary parameter @delalloc_start for writepage_delalloc() Qu Wenruo
2021-07-13  6:14 ` Qu Wenruo [this message]
2021-07-13  7:36   ` [PATCH 03/27] btrfs: use async_chunk::async_cow to replace the confusing pending pointer Nikolay Borisov
2021-07-13  6:14 ` [PATCH 04/27] btrfs: don't pass compressed pages to btrfs_writepage_endio_finish_ordered() Qu Wenruo
2021-07-13  6:14 ` [PATCH 05/27] btrfs: make add_ra_bio_pages() to be subpage compatible Qu Wenruo
2021-07-13  6:14 ` [PATCH 06/27] btrfs: introduce compressed_bio::pending_sectors to trace compressed bio more elegantly Qu Wenruo
2021-07-13  6:14 ` [PATCH 07/27] btrfs: add subpage checked_bitmap to make PageChecked flag to be subpage compatible Qu Wenruo
2021-07-16  7:54   ` Qu Wenruo
2021-07-13  6:14 ` [PATCH 08/27] btrfs: handle errors properly inside btrfs_submit_compressed_read() Qu Wenruo
2021-07-13  6:14 ` [PATCH 09/27] btrfs: handle errors properly inside btrfs_submit_compressed_write() Qu Wenruo
2021-07-13  6:14 ` [PATCH 10/27] btrfs: introduce submit_compressed_bio() for compression Qu Wenruo
2021-07-13  6:15 ` [PATCH 11/27] btrfs: introduce alloc_compressed_bio() " Qu Wenruo
2021-07-13  6:15 ` [PATCH 12/27] btrfs: make btrfs_submit_compressed_read() to determine stripe boundary at bio allocation time Qu Wenruo
2021-07-13  6:15 ` [PATCH 13/27] btrfs: make btrfs_submit_compressed_write() " Qu Wenruo
2021-07-13  6:15 ` [PATCH 14/27] btrfs: remove unused function btrfs_bio_fits_in_stripe() Qu Wenruo
2021-07-13  6:15 ` [PATCH 15/27] btrfs: refactor submit_compressed_extents() Qu Wenruo
2021-07-13  6:15 ` [PATCH 16/27] btrfs: cleanup for extent_write_locked_range() Qu Wenruo
2021-07-13  6:15 ` [PATCH 17/27] btrfs: make compress_file_range() to be subpage compatible Qu Wenruo
2021-07-13  6:15 ` [PATCH 18/27] btrfs: make btrfs_submit_compressed_write() " Qu Wenruo
2021-07-13  6:15 ` [PATCH 19/27] btrfs: make end_compressed_bio_writeback() to be subpage compatble Qu Wenruo
2021-07-13  6:15 ` [PATCH 20/27] btrfs: make extent_write_locked_range() to be subpage compatible Qu Wenruo
2021-07-13  6:15 ` [PATCH 21/27] btrfs: extract uncompressed async extent submission code into a new helper Qu Wenruo
2021-07-13  6:15 ` [PATCH 22/27] btrfs: rework lzo_compress_pages() to make it subpage compatible Qu Wenruo
2021-07-13  6:15 ` [PATCH 23/27] btrfs: teach __extent_writepage() to handle locked page differently Qu Wenruo
2021-07-13  6:15 ` [PATCH 24/27] btrfs: allow page to be unlocked by btrfs_page_end_writer_lock() even if it's locked by plain page_lock() Qu Wenruo
2021-07-13  6:15 ` [PATCH 25/27] btrfs: allow subpage to compress a range which only covers one page Qu Wenruo
2021-07-13  6:15 ` [PATCH 26/27] btrfs: don't run delalloc range which is beyond the locked_page to prevent deadlock for subpage compression Qu Wenruo
2021-07-13  6:15 ` [PATCH 27/27] btrfs: only allow subpage compression if the range is fully page aligned Qu Wenruo
2021-07-16  9:11 ` [PATCH 00/27] btrfs: limited subpage compressed write support Qu Wenruo
2021-07-20  5:00   ` Qu Wenruo

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