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Commit eef16ba2 authored by Kuanling Huang's avatar Kuanling Huang Committed by David Sterba
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Btrfs: send, apply asynchronous page cache readahead to enhance page read 



By analyzing the perf on btrfs send, we found it take large amount of
cpu time on page_cache_sync_readahead. This effort can be reduced after
switching to asynchronous one. Overall performance gain on HDD and SSD
were 9 and 15 percent if simply send a large file.

Signed-off-by: default avatarKuanling Huang <peterh@synology.com>
Reviewed-by: default avatarNikolay Borisov <nborisov@suse.com>
Reviewed-by: default avatarDavid Sterba <dsterba@suse.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent 785884fc

fs/btrfs/send.c

+16 −5
Original line number Original line Diff line number Diff line
@@ -4720,17 +4720,28 @@ static ssize_t fill_read_buf(struct send_ctx *sctx, u64 offset, u32 len) 
	/* initial readahead */

	/* initial readahead */

	memset(&sctx->ra, 0, sizeof(struct file_ra_state));

	memset(&sctx->ra, 0, sizeof(struct file_ra_state));

	file_ra_state_init(&sctx->ra, inode->i_mapping);

	file_ra_state_init(&sctx->ra, inode->i_mapping);

	page_cache_sync_readahead(inode->i_mapping, &sctx->ra, NULL, index,

		       last_index - index + 1);





	while (index <= last_index) {

	while (index <= last_index) {

		unsigned cur_len = min_t(unsigned, len,

		unsigned cur_len = min_t(unsigned, len,

					 PAGE_SIZE - pg_offset);

					 PAGE_SIZE - pg_offset);

		page = find_or_create_page(inode->i_mapping, index, GFP_KERNEL);



		page = find_lock_page(inode->i_mapping, index);

		if (!page) {

			page_cache_sync_readahead(inode->i_mapping, &sctx->ra,

				NULL, index, last_index + 1 - index);



			page = find_or_create_page(inode->i_mapping, index,

					GFP_KERNEL);

			if (!page) {

			if (!page) {

				ret = -ENOMEM;

				ret = -ENOMEM;

				break;

				break;

			}

			}

		}



		if (PageReadahead(page)) {

			page_cache_async_readahead(inode->i_mapping, &sctx->ra,

				NULL, page, index, last_index + 1 - index);

		}





		if (!PageUptodate(page)) {

		if (!PageUptodate(page)) {

			btrfs_readpage(NULL, page);

			btrfs_readpage(NULL, page);