ext4: make ext4_bio_write_page() use BH_Async_Write flags
So far ext4_bio_write_page() attached all the pages to ext4_io_end
structure. This makes that structure pretty heavy (1 KB for pointers
+ 16 bytes per page attached to the bio). Also later we would like to
share ext4_io_end structure among several bios in case IO to a single
extent needs to be split among several bios and pointing to pages from
ext4_io_end makes this complex.
We remove page pointers from ext4_io_end and use pointers from bio
itself instead. This isn't as easy when blocksize < pagesize because
then we can have several bios in flight for a single page and we have
to be careful when to call end_page_writeback(). However this is a
known problem already solved by block_write_full_page() /
end_buffer_async_write() so we mimic its behavior here. We mark
buffers going to disk with BH_Async_Write flag and in
ext4_bio_end_io() we check whether there are any buffers with
BH_Async_Write flag left. If there are not, we can call
end_page_writeback().
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Reviewed-by: Dmitry Monakhov <dmonakhov@openvz.org>
Reviewed-by: Zheng Liu <wenqing.lz@taobao.com>
diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
index 047a6de..1d98fcf 100644
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -29,25 +29,19 @@
#include "xattr.h"
#include "acl.h"
-static struct kmem_cache *io_page_cachep, *io_end_cachep;
+static struct kmem_cache *io_end_cachep;
int __init ext4_init_pageio(void)
{
- io_page_cachep = KMEM_CACHE(ext4_io_page, SLAB_RECLAIM_ACCOUNT);
- if (io_page_cachep == NULL)
- return -ENOMEM;
io_end_cachep = KMEM_CACHE(ext4_io_end, SLAB_RECLAIM_ACCOUNT);
- if (io_end_cachep == NULL) {
- kmem_cache_destroy(io_page_cachep);
+ if (io_end_cachep == NULL)
return -ENOMEM;
- }
return 0;
}
void ext4_exit_pageio(void)
{
kmem_cache_destroy(io_end_cachep);
- kmem_cache_destroy(io_page_cachep);
}
/*
@@ -67,15 +61,6 @@
cancel_work_sync(&EXT4_I(inode)->i_unwritten_work);
}
-static void put_io_page(struct ext4_io_page *io_page)
-{
- if (atomic_dec_and_test(&io_page->p_count)) {
- end_page_writeback(io_page->p_page);
- put_page(io_page->p_page);
- kmem_cache_free(io_page_cachep, io_page);
- }
-}
-
void ext4_free_io_end(ext4_io_end_t *io)
{
int i;
@@ -84,9 +69,6 @@
BUG_ON(!list_empty(&io->list));
BUG_ON(io->flag & EXT4_IO_END_UNWRITTEN);
- for (i = 0; i < io->num_io_pages; i++)
- put_io_page(io->pages[i]);
- io->num_io_pages = 0;
if (atomic_dec_and_test(&EXT4_I(io->inode)->i_ioend_count))
wake_up_all(ext4_ioend_wq(io->inode));
kmem_cache_free(io_end_cachep, io);
@@ -243,45 +225,56 @@
ext4_io_end_t *io_end = bio->bi_private;
struct inode *inode;
int i;
+ int blocksize;
sector_t bi_sector = bio->bi_sector;
BUG_ON(!io_end);
+ inode = io_end->inode;
+ blocksize = 1 << inode->i_blkbits;
bio->bi_private = NULL;
bio->bi_end_io = NULL;
if (test_bit(BIO_UPTODATE, &bio->bi_flags))
error = 0;
- bio_put(bio);
-
- for (i = 0; i < io_end->num_io_pages; i++) {
- struct page *page = io_end->pages[i]->p_page;
+ for (i = 0; i < bio->bi_vcnt; i++) {
+ struct bio_vec *bvec = &bio->bi_io_vec[i];
+ struct page *page = bvec->bv_page;
struct buffer_head *bh, *head;
- loff_t offset;
- loff_t io_end_offset;
+ unsigned bio_start = bvec->bv_offset;
+ unsigned bio_end = bio_start + bvec->bv_len;
+ unsigned under_io = 0;
+ unsigned long flags;
+
+ if (!page)
+ continue;
if (error) {
SetPageError(page);
set_bit(AS_EIO, &page->mapping->flags);
- head = page_buffers(page);
- BUG_ON(!head);
-
- io_end_offset = io_end->offset + io_end->size;
-
- offset = (sector_t) page->index << PAGE_CACHE_SHIFT;
- bh = head;
- do {
- if ((offset >= io_end->offset) &&
- (offset+bh->b_size <= io_end_offset))
- buffer_io_error(bh);
-
- offset += bh->b_size;
- bh = bh->b_this_page;
- } while (bh != head);
}
-
- put_io_page(io_end->pages[i]);
+ bh = head = page_buffers(page);
+ /*
+ * We check all buffers in the page under BH_Uptodate_Lock
+ * to avoid races with other end io clearing async_write flags
+ */
+ local_irq_save(flags);
+ bit_spin_lock(BH_Uptodate_Lock, &head->b_state);
+ do {
+ if (bh_offset(bh) < bio_start ||
+ bh_offset(bh) + blocksize > bio_end) {
+ if (buffer_async_write(bh))
+ under_io++;
+ continue;
+ }
+ clear_buffer_async_write(bh);
+ if (error)
+ buffer_io_error(bh);
+ } while ((bh = bh->b_this_page) != head);
+ bit_spin_unlock(BH_Uptodate_Lock, &head->b_state);
+ local_irq_restore(flags);
+ if (!under_io)
+ end_page_writeback(page);
}
- io_end->num_io_pages = 0;
- inode = io_end->inode;
+ bio_put(bio);
if (error) {
io_end->flag |= EXT4_IO_END_ERROR;
@@ -345,7 +338,6 @@
}
static int io_submit_add_bh(struct ext4_io_submit *io,
- struct ext4_io_page *io_page,
struct inode *inode,
struct writeback_control *wbc,
struct buffer_head *bh)
@@ -353,11 +345,6 @@
ext4_io_end_t *io_end;
int ret;
- if (buffer_new(bh)) {
- clear_buffer_new(bh);
- unmap_underlying_metadata(bh->b_bdev, bh->b_blocknr);
- }
-
if (io->io_bio && bh->b_blocknr != io->io_next_block) {
submit_and_retry:
ext4_io_submit(io);
@@ -368,9 +355,6 @@
return ret;
}
io_end = io->io_end;
- if ((io_end->num_io_pages >= MAX_IO_PAGES) &&
- (io_end->pages[io_end->num_io_pages-1] != io_page))
- goto submit_and_retry;
if (buffer_uninit(bh))
ext4_set_io_unwritten_flag(inode, io_end);
io->io_end->size += bh->b_size;
@@ -378,11 +362,6 @@
ret = bio_add_page(io->io_bio, bh->b_page, bh->b_size, bh_offset(bh));
if (ret != bh->b_size)
goto submit_and_retry;
- if ((io_end->num_io_pages == 0) ||
- (io_end->pages[io_end->num_io_pages-1] != io_page)) {
- io_end->pages[io_end->num_io_pages++] = io_page;
- atomic_inc(&io_page->p_count);
- }
return 0;
}
@@ -392,33 +371,29 @@
struct writeback_control *wbc)
{
struct inode *inode = page->mapping->host;
- unsigned block_start, block_end, blocksize;
- struct ext4_io_page *io_page;
+ unsigned block_start, blocksize;
struct buffer_head *bh, *head;
int ret = 0;
+ int nr_submitted = 0;
blocksize = 1 << inode->i_blkbits;
BUG_ON(!PageLocked(page));
BUG_ON(PageWriteback(page));
- io_page = kmem_cache_alloc(io_page_cachep, GFP_NOFS);
- if (!io_page) {
- redirty_page_for_writepage(wbc, page);
- unlock_page(page);
- return -ENOMEM;
- }
- io_page->p_page = page;
- atomic_set(&io_page->p_count, 1);
- get_page(page);
set_page_writeback(page);
ClearPageError(page);
- for (bh = head = page_buffers(page), block_start = 0;
- bh != head || !block_start;
- block_start = block_end, bh = bh->b_this_page) {
-
- block_end = block_start + blocksize;
+ /*
+ * In the first loop we prepare and mark buffers to submit. We have to
+ * mark all buffers in the page before submitting so that
+ * end_page_writeback() cannot be called from ext4_bio_end_io() when IO
+ * on the first buffer finishes and we are still working on submitting
+ * the second buffer.
+ */
+ bh = head = page_buffers(page);
+ do {
+ block_start = bh_offset(bh);
if (block_start >= len) {
/*
* Comments copied from block_write_full_page_endio:
@@ -431,7 +406,8 @@
* mapped, and writes to that region are not written
* out to the file."
*/
- zero_user_segment(page, block_start, block_end);
+ zero_user_segment(page, block_start,
+ block_start + blocksize);
clear_buffer_dirty(bh);
set_buffer_uptodate(bh);
continue;
@@ -445,7 +421,19 @@
ext4_io_submit(io);
continue;
}
- ret = io_submit_add_bh(io, io_page, inode, wbc, bh);
+ if (buffer_new(bh)) {
+ clear_buffer_new(bh);
+ unmap_underlying_metadata(bh->b_bdev, bh->b_blocknr);
+ }
+ set_buffer_async_write(bh);
+ } while ((bh = bh->b_this_page) != head);
+
+ /* Now submit buffers to write */
+ bh = head = page_buffers(page);
+ do {
+ if (!buffer_async_write(bh))
+ continue;
+ ret = io_submit_add_bh(io, inode, wbc, bh);
if (ret) {
/*
* We only get here on ENOMEM. Not much else
@@ -455,17 +443,20 @@
redirty_page_for_writepage(wbc, page);
break;
}
+ nr_submitted++;
clear_buffer_dirty(bh);
+ } while ((bh = bh->b_this_page) != head);
+
+ /* Error stopped previous loop? Clean up buffers... */
+ if (ret) {
+ do {
+ clear_buffer_async_write(bh);
+ bh = bh->b_this_page;
+ } while (bh != head);
}
unlock_page(page);
- /*
- * If the page was truncated before we could do the writeback,
- * or we had a memory allocation error while trying to write
- * the first buffer head, we won't have submitted any pages for
- * I/O. In that case we need to make sure we've cleared the
- * PageWriteback bit from the page to prevent the system from
- * wedging later on.
- */
- put_io_page(io_page);
+ /* Nothing submitted - we have to end page writeback */
+ if (!nr_submitted)
+ end_page_writeback(page);
return ret;
}
