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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>
This commit is contained in:
Jan Kara
Theodore Ts'o
parent
e1091b157c
commit
0058f9658c
@ -198,19 +198,8 @@ struct mpage_da_data {
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#define EXT4_IO_END_ERROR 0x0002
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#define EXT4_IO_END_DIRECT 0x0004
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struct ext4_io_page {
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struct page *p_page;
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atomic_t p_count;
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};
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#define MAX_IO_PAGES 128
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/*
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* For converting uninitialized extents on a work queue.
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*
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* 'page' is only used from the writepage() path; 'pages' is only used for
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* buffered writes; they are used to keep page references until conversion
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* takes place. For AIO/DIO, neither field is filled in.
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*/
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typedef struct ext4_io_end {
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struct list_head list; /* per-file finished IO list */
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@ -220,15 +209,12 @@ typedef struct ext4_io_end {
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ssize_t size; /* size of the extent */
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struct kiocb *iocb; /* iocb struct for AIO */
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int result; /* error value for AIO */
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int num_io_pages; /* for writepages() */
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struct ext4_io_page *pages[MAX_IO_PAGES]; /* for writepages() */
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} ext4_io_end_t;
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struct ext4_io_submit {
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int io_op;
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struct bio *io_bio;
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ext4_io_end_t *io_end;
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struct ext4_io_page *io_page;
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sector_t io_next_block;
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};
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@ -29,25 +29,19 @@
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#include "xattr.h"
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#include "acl.h"
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static struct kmem_cache *io_page_cachep, *io_end_cachep;
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static struct kmem_cache *io_end_cachep;
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int __init ext4_init_pageio(void)
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{
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io_page_cachep = KMEM_CACHE(ext4_io_page, SLAB_RECLAIM_ACCOUNT);
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if (io_page_cachep == NULL)
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return -ENOMEM;
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io_end_cachep = KMEM_CACHE(ext4_io_end, SLAB_RECLAIM_ACCOUNT);
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if (io_end_cachep == NULL) {
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kmem_cache_destroy(io_page_cachep);
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if (io_end_cachep == NULL)
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return -ENOMEM;
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}
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return 0;
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}
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void ext4_exit_pageio(void)
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{
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kmem_cache_destroy(io_end_cachep);
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kmem_cache_destroy(io_page_cachep);
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}
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/*
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@ -67,15 +61,6 @@ void ext4_ioend_shutdown(struct inode *inode)
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cancel_work_sync(&EXT4_I(inode)->i_unwritten_work);
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}
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static void put_io_page(struct ext4_io_page *io_page)
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{
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if (atomic_dec_and_test(&io_page->p_count)) {
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end_page_writeback(io_page->p_page);
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put_page(io_page->p_page);
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kmem_cache_free(io_page_cachep, io_page);
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}
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}
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void ext4_free_io_end(ext4_io_end_t *io)
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{
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int i;
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@ -84,9 +69,6 @@ void ext4_free_io_end(ext4_io_end_t *io)
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BUG_ON(!list_empty(&io->list));
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BUG_ON(io->flag & EXT4_IO_END_UNWRITTEN);
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for (i = 0; i < io->num_io_pages; i++)
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put_io_page(io->pages[i]);
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io->num_io_pages = 0;
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if (atomic_dec_and_test(&EXT4_I(io->inode)->i_ioend_count))
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wake_up_all(ext4_ioend_wq(io->inode));
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kmem_cache_free(io_end_cachep, io);
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@ -243,45 +225,56 @@ static void ext4_end_bio(struct bio *bio, int error)
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ext4_io_end_t *io_end = bio->bi_private;
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struct inode *inode;
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int i;
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int blocksize;
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sector_t bi_sector = bio->bi_sector;
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BUG_ON(!io_end);
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inode = io_end->inode;
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blocksize = 1 << inode->i_blkbits;
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bio->bi_private = NULL;
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bio->bi_end_io = NULL;
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if (test_bit(BIO_UPTODATE, &bio->bi_flags))
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error = 0;
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bio_put(bio);
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for (i = 0; i < io_end->num_io_pages; i++) {
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struct page *page = io_end->pages[i]->p_page;
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for (i = 0; i < bio->bi_vcnt; i++) {
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struct bio_vec *bvec = &bio->bi_io_vec[i];
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struct page *page = bvec->bv_page;
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struct buffer_head *bh, *head;
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loff_t offset;
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loff_t io_end_offset;
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unsigned bio_start = bvec->bv_offset;
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unsigned bio_end = bio_start + bvec->bv_len;
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unsigned under_io = 0;
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unsigned long flags;
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if (!page)
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continue;
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if (error) {
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SetPageError(page);
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set_bit(AS_EIO, &page->mapping->flags);
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head = page_buffers(page);
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BUG_ON(!head);
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io_end_offset = io_end->offset + io_end->size;
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offset = (sector_t) page->index << PAGE_CACHE_SHIFT;
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bh = head;
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do {
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if ((offset >= io_end->offset) &&
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(offset+bh->b_size <= io_end_offset))
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buffer_io_error(bh);
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offset += bh->b_size;
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bh = bh->b_this_page;
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} while (bh != head);
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}
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put_io_page(io_end->pages[i]);
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bh = head = page_buffers(page);
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/*
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* We check all buffers in the page under BH_Uptodate_Lock
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* to avoid races with other end io clearing async_write flags
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*/
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local_irq_save(flags);
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bit_spin_lock(BH_Uptodate_Lock, &head->b_state);
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do {
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if (bh_offset(bh) < bio_start ||
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bh_offset(bh) + blocksize > bio_end) {
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if (buffer_async_write(bh))
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under_io++;
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continue;
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}
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clear_buffer_async_write(bh);
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if (error)
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buffer_io_error(bh);
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} while ((bh = bh->b_this_page) != head);
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bit_spin_unlock(BH_Uptodate_Lock, &head->b_state);
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local_irq_restore(flags);
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if (!under_io)
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end_page_writeback(page);
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}
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io_end->num_io_pages = 0;
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inode = io_end->inode;
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bio_put(bio);
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if (error) {
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io_end->flag |= EXT4_IO_END_ERROR;
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@ -345,7 +338,6 @@ static int io_submit_init(struct ext4_io_submit *io,
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}
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static int io_submit_add_bh(struct ext4_io_submit *io,
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struct ext4_io_page *io_page,
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struct inode *inode,
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struct writeback_control *wbc,
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struct buffer_head *bh)
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@ -353,11 +345,6 @@ static int io_submit_add_bh(struct ext4_io_submit *io,
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ext4_io_end_t *io_end;
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int ret;
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if (buffer_new(bh)) {
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clear_buffer_new(bh);
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unmap_underlying_metadata(bh->b_bdev, bh->b_blocknr);
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}
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if (io->io_bio && bh->b_blocknr != io->io_next_block) {
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submit_and_retry:
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ext4_io_submit(io);
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@ -368,9 +355,6 @@ submit_and_retry:
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return ret;
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}
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io_end = io->io_end;
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if ((io_end->num_io_pages >= MAX_IO_PAGES) &&
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(io_end->pages[io_end->num_io_pages-1] != io_page))
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goto submit_and_retry;
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if (buffer_uninit(bh))
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ext4_set_io_unwritten_flag(inode, io_end);
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io->io_end->size += bh->b_size;
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@ -378,11 +362,6 @@ submit_and_retry:
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ret = bio_add_page(io->io_bio, bh->b_page, bh->b_size, bh_offset(bh));
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if (ret != bh->b_size)
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goto submit_and_retry;
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if ((io_end->num_io_pages == 0) ||
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(io_end->pages[io_end->num_io_pages-1] != io_page)) {
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io_end->pages[io_end->num_io_pages++] = io_page;
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atomic_inc(&io_page->p_count);
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}
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return 0;
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}
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@ -392,33 +371,29 @@ int ext4_bio_write_page(struct ext4_io_submit *io,
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struct writeback_control *wbc)
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{
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struct inode *inode = page->mapping->host;
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unsigned block_start, block_end, blocksize;
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struct ext4_io_page *io_page;
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unsigned block_start, blocksize;
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struct buffer_head *bh, *head;
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int ret = 0;
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int nr_submitted = 0;
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blocksize = 1 << inode->i_blkbits;
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BUG_ON(!PageLocked(page));
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BUG_ON(PageWriteback(page));
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io_page = kmem_cache_alloc(io_page_cachep, GFP_NOFS);
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if (!io_page) {
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redirty_page_for_writepage(wbc, page);
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unlock_page(page);
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return -ENOMEM;
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}
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io_page->p_page = page;
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atomic_set(&io_page->p_count, 1);
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get_page(page);
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set_page_writeback(page);
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ClearPageError(page);
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for (bh = head = page_buffers(page), block_start = 0;
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bh != head || !block_start;
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block_start = block_end, bh = bh->b_this_page) {
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block_end = block_start + blocksize;
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/*
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* In the first loop we prepare and mark buffers to submit. We have to
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* mark all buffers in the page before submitting so that
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* end_page_writeback() cannot be called from ext4_bio_end_io() when IO
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* on the first buffer finishes and we are still working on submitting
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* the second buffer.
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*/
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bh = head = page_buffers(page);
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do {
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block_start = bh_offset(bh);
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if (block_start >= len) {
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/*
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* Comments copied from block_write_full_page_endio:
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@ -431,7 +406,8 @@ int ext4_bio_write_page(struct ext4_io_submit *io,
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* mapped, and writes to that region are not written
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* out to the file."
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*/
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zero_user_segment(page, block_start, block_end);
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zero_user_segment(page, block_start,
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block_start + blocksize);
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clear_buffer_dirty(bh);
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set_buffer_uptodate(bh);
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continue;
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@ -445,7 +421,19 @@ int ext4_bio_write_page(struct ext4_io_submit *io,
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ext4_io_submit(io);
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continue;
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}
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ret = io_submit_add_bh(io, io_page, inode, wbc, bh);
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if (buffer_new(bh)) {
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clear_buffer_new(bh);
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unmap_underlying_metadata(bh->b_bdev, bh->b_blocknr);
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}
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set_buffer_async_write(bh);
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} while ((bh = bh->b_this_page) != head);
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/* Now submit buffers to write */
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bh = head = page_buffers(page);
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do {
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if (!buffer_async_write(bh))
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continue;
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ret = io_submit_add_bh(io, inode, wbc, bh);
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if (ret) {
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/*
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* We only get here on ENOMEM. Not much else
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@ -455,17 +443,20 @@ int ext4_bio_write_page(struct ext4_io_submit *io,
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redirty_page_for_writepage(wbc, page);
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break;
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}
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nr_submitted++;
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clear_buffer_dirty(bh);
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} while ((bh = bh->b_this_page) != head);
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/* Error stopped previous loop? Clean up buffers... */
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if (ret) {
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do {
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clear_buffer_async_write(bh);
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bh = bh->b_this_page;
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} while (bh != head);
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}
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unlock_page(page);
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/*
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* If the page was truncated before we could do the writeback,
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* or we had a memory allocation error while trying to write
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* the first buffer head, we won't have submitted any pages for
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* I/O. In that case we need to make sure we've cleared the
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* PageWriteback bit from the page to prevent the system from
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* wedging later on.
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*/
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put_io_page(io_page);
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/* Nothing submitted - we have to end page writeback */
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if (!nr_submitted)
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end_page_writeback(page);
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return ret;
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}
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