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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: 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>
This commit is contained in:
Kuanling Huang 2017-09-15 16:47:45 +08:00 committed by David Sterba
parent 785884fc31
commit eef16ba269
1 changed files with 16 additions and 5 deletions
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21
fs/btrfs/send.c
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@ -4720,16 +4720,27 @@ 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) {
ret = -ENOMEM;
break;
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)) {