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btrfs: always read the entire extent_buffer

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Currently read_extent_buffer_pages skips pages that are already uptodate
when reading in an extent_buffer.  While this reduces the amount of data
read, it increases the number of I/O operations as we now need to do
multiple I/Os when reading an extent buffer with one or more uptodate
pages in the middle of it.  On any modern storage device, be that hard
drives or SSDs this actually decreases I/O performance.  Fortunately
this case is pretty rare as the pages are always initially read together
and then aged the same way.  Besides simplifying the code a bit as-is
this will allow for major simplifications to the I/O completion handler
later on.

Note that the case where all pages are uptodate is still handled by an
optimized fast path that does not read any data from disk.

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Christoph Hellwig 2023-05-03 17:24:25 +02:00 committed by David Sterba
parent d87e6575e9
commit e95382834c
1 changed files with 5 additions and 12 deletions
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17
fs/btrfs/extent_io.c
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@ -4315,7 +4315,6 @@ int read_extent_buffer_pages(struct extent_buffer *eb, int wait, int mirror_num,
int locked_pages = 0;
int all_uptodate = 1;
int num_pages;
unsigned long num_reads = 0;
struct btrfs_bio_ctrl bio_ctrl = {
.opf = REQ_OP_READ,
.mirror_num = mirror_num,
@ -4361,10 +4360,8 @@ int read_extent_buffer_pages(struct extent_buffer *eb, int wait, int mirror_num,
*/
for (i = 0; i < num_pages; i++) {
page = eb->pages[i];
if (!PageUptodate(page)) {
num_reads++;
if (!PageUptodate(page))
all_uptodate = 0;
}
}
if (all_uptodate) {
@ -4374,7 +4371,7 @@ int read_extent_buffer_pages(struct extent_buffer *eb, int wait, int mirror_num,
clear_bit(EXTENT_BUFFER_READ_ERR, &eb->bflags);
eb->read_mirror = 0;
atomic_set(&eb->io_pages, num_reads);
atomic_set(&eb->io_pages, num_pages);
/*
* It is possible for release_folio to clear the TREE_REF bit before we
* set io_pages. See check_buffer_tree_ref for a more detailed comment.
@ -4384,13 +4381,9 @@ int read_extent_buffer_pages(struct extent_buffer *eb, int wait, int mirror_num,
for (i = 0; i < num_pages; i++) {
page = eb->pages[i];
if (!PageUptodate(page)) {
ClearPageError(page);
submit_extent_page(&bio_ctrl, page_offset(page), page,
PAGE_SIZE, 0);
} else {
unlock_page(page);
}
ClearPageError(page);
submit_extent_page(&bio_ctrl, page_offset(page), page,
PAGE_SIZE, 0);
}
submit_one_bio(&bio_ctrl);