Btrfs: send, apply asynchronous page cache readahead to enhance page read (eef16ba2) · Commits · 戴 / test

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:

Kuanling Huang <peterh@synology.com> Reviewed-by:

Nikolay Borisov <nborisov@suse.com> Reviewed-by:

David Sterba <dsterba@suse.com> Signed-off-by:

David Sterba <dsterba@suse.com>

fs/btrfs/send.c

+16 −5

Original line number	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 */
		memset(&sctx->ra, 0, sizeof(struct file_ra_state));
		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) {
		unsigned cur_len = min_t(unsigned, len,
		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) {
		ret = -ENOMEM;
		break;
		}
		}

		if (PageReadahead(page)) {
		page_cache_async_readahead(inode->i_mapping, &sctx->ra,
		NULL, page, index, last_index + 1 - index);
		}

		if (!PageUptodate(page)) {
		btrfs_readpage(NULL, page);

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