xfs: stop using the page cache to back the buffer cache
Now that the buffer cache has it's own LRU, we do not need to use
the page cache to provide persistent caching and reclaim
infrastructure. Convert the buffer cache to use alloc_pages()
instead of the page cache. This will remove all the overhead of page
cache management from setup and teardown of the buffers, as well as
needing to mark pages accessed as we find buffers in the buffer
cache.
By avoiding the page cache, we also remove the need to keep state in
the page_private(page) field for persistant storage across buffer
free/buffer rebuild and so all that code can be removed. This also
fixes the long-standing problem of not having enough bits in the
page_private field to track all the state needed for a 512
sector/64k page setup.
It also removes the need for page locking during reads as the pages
are unique to the buffer and nobody else will be attempting to
access them.
Finally, it removes the buftarg address space lock as a point of
global contention on workloads that allocate and free buffers
quickly such as when creating or removing large numbers of inodes in
parallel. This remove the 16TB limit on filesystem size on 32 bit
machines as the page index (32 bit) is no longer used for lookups
of metadata buffers - the buffer cache is now solely indexed by disk
address which is stored in a 64 bit field in the buffer.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Alex Elder <aelder@sgi.com>
diff --git a/fs/xfs/linux-2.6/xfs_buf.c b/fs/xfs/linux-2.6/xfs_buf.c
index a5a260f..d45b2cd 100644
--- a/fs/xfs/linux-2.6/xfs_buf.c
+++ b/fs/xfs/linux-2.6/xfs_buf.c
@@ -94,75 +94,6 @@
}
/*
- * Page Region interfaces.
- *
- * For pages in filesystems where the blocksize is smaller than the
- * pagesize, we use the page->private field (long) to hold a bitmap
- * of uptodate regions within the page.
- *
- * Each such region is "bytes per page / bits per long" bytes long.
- *
- * NBPPR == number-of-bytes-per-page-region
- * BTOPR == bytes-to-page-region (rounded up)
- * BTOPRT == bytes-to-page-region-truncated (rounded down)
- */
-#if (BITS_PER_LONG == 32)
-#define PRSHIFT (PAGE_CACHE_SHIFT - 5) /* (32 == 1<<5) */
-#elif (BITS_PER_LONG == 64)
-#define PRSHIFT (PAGE_CACHE_SHIFT - 6) /* (64 == 1<<6) */
-#else
-#error BITS_PER_LONG must be 32 or 64
-#endif
-#define NBPPR (PAGE_CACHE_SIZE/BITS_PER_LONG)
-#define BTOPR(b) (((unsigned int)(b) + (NBPPR - 1)) >> PRSHIFT)
-#define BTOPRT(b) (((unsigned int)(b) >> PRSHIFT))
-
-STATIC unsigned long
-page_region_mask(
- size_t offset,
- size_t length)
-{
- unsigned long mask;
- int first, final;
-
- first = BTOPR(offset);
- final = BTOPRT(offset + length - 1);
- first = min(first, final);
-
- mask = ~0UL;
- mask <<= BITS_PER_LONG - (final - first);
- mask >>= BITS_PER_LONG - (final);
-
- ASSERT(offset + length <= PAGE_CACHE_SIZE);
- ASSERT((final - first) < BITS_PER_LONG && (final - first) >= 0);
-
- return mask;
-}
-
-STATIC void
-set_page_region(
- struct page *page,
- size_t offset,
- size_t length)
-{
- set_page_private(page,
- page_private(page) | page_region_mask(offset, length));
- if (page_private(page) == ~0UL)
- SetPageUptodate(page);
-}
-
-STATIC int
-test_page_region(
- struct page *page,
- size_t offset,
- size_t length)
-{
- unsigned long mask = page_region_mask(offset, length);
-
- return (mask && (page_private(page) & mask) == mask);
-}
-
-/*
* xfs_buf_lru_add - add a buffer to the LRU.
*
* The LRU takes a new reference to the buffer so that it will only be freed
@@ -332,7 +263,7 @@
ASSERT(list_empty(&bp->b_lru));
- if (bp->b_flags & (_XBF_PAGE_CACHE|_XBF_PAGES)) {
+ if (bp->b_flags & _XBF_PAGES) {
uint i;
if (xfs_buf_is_vmapped(bp))
@@ -342,25 +273,22 @@
for (i = 0; i < bp->b_page_count; i++) {
struct page *page = bp->b_pages[i];
- if (bp->b_flags & _XBF_PAGE_CACHE)
- ASSERT(!PagePrivate(page));
- page_cache_release(page);
+ __free_page(page);
}
- }
+ } else if (bp->b_flags & _XBF_KMEM)
+ kmem_free(bp->b_addr);
_xfs_buf_free_pages(bp);
xfs_buf_deallocate(bp);
}
/*
- * Finds all pages for buffer in question and builds it's page list.
+ * Allocates all the pages for buffer in question and builds it's page list.
*/
STATIC int
-_xfs_buf_lookup_pages(
+xfs_buf_allocate_memory(
xfs_buf_t *bp,
uint flags)
{
- struct address_space *mapping = bp->b_target->bt_mapping;
- size_t blocksize = bp->b_target->bt_bsize;
size_t size = bp->b_count_desired;
size_t nbytes, offset;
gfp_t gfp_mask = xb_to_gfp(flags);
@@ -369,29 +297,55 @@
xfs_off_t end;
int error;
+ /*
+ * for buffers that are contained within a single page, just allocate
+ * the memory from the heap - there's no need for the complexity of
+ * page arrays to keep allocation down to order 0.
+ */
+ if (bp->b_buffer_length < PAGE_SIZE) {
+ bp->b_addr = kmem_alloc(bp->b_buffer_length, xb_to_km(flags));
+ if (!bp->b_addr) {
+ /* low memory - use alloc_page loop instead */
+ goto use_alloc_page;
+ }
+
+ if (((unsigned long)(bp->b_addr + bp->b_buffer_length - 1) &
+ PAGE_MASK) !=
+ ((unsigned long)bp->b_addr & PAGE_MASK)) {
+ /* b_addr spans two pages - use alloc_page instead */
+ kmem_free(bp->b_addr);
+ bp->b_addr = NULL;
+ goto use_alloc_page;
+ }
+ bp->b_offset = offset_in_page(bp->b_addr);
+ bp->b_pages = bp->b_page_array;
+ bp->b_pages[0] = virt_to_page(bp->b_addr);
+ bp->b_page_count = 1;
+ bp->b_flags |= XBF_MAPPED | _XBF_KMEM;
+ return 0;
+ }
+
+use_alloc_page:
end = bp->b_file_offset + bp->b_buffer_length;
page_count = xfs_buf_btoc(end) - xfs_buf_btoct(bp->b_file_offset);
-
error = _xfs_buf_get_pages(bp, page_count, flags);
if (unlikely(error))
return error;
- bp->b_flags |= _XBF_PAGE_CACHE;
offset = bp->b_offset;
- first = bp->b_file_offset >> PAGE_CACHE_SHIFT;
+ first = bp->b_file_offset >> PAGE_SHIFT;
+ bp->b_flags |= _XBF_PAGES;
for (i = 0; i < bp->b_page_count; i++) {
struct page *page;
uint retries = 0;
-
- retry:
- page = find_or_create_page(mapping, first + i, gfp_mask);
+retry:
+ page = alloc_page(gfp_mask);
if (unlikely(page == NULL)) {
if (flags & XBF_READ_AHEAD) {
bp->b_page_count = i;
- for (i = 0; i < bp->b_page_count; i++)
- unlock_page(bp->b_pages[i]);
- return -ENOMEM;
+ error = ENOMEM;
+ goto out_free_pages;
}
/*
@@ -412,33 +366,16 @@
XFS_STATS_INC(xb_page_found);
- nbytes = min_t(size_t, size, PAGE_CACHE_SIZE - offset);
+ nbytes = min_t(size_t, size, PAGE_SIZE - offset);
size -= nbytes;
-
- ASSERT(!PagePrivate(page));
- if (!PageUptodate(page)) {
- page_count--;
- if (blocksize >= PAGE_CACHE_SIZE) {
- if (flags & XBF_READ)
- bp->b_flags |= _XBF_PAGE_LOCKED;
- } else if (!PagePrivate(page)) {
- if (test_page_region(page, offset, nbytes))
- page_count++;
- }
- }
-
bp->b_pages[i] = page;
offset = 0;
}
+ return 0;
- if (!(bp->b_flags & _XBF_PAGE_LOCKED)) {
- for (i = 0; i < bp->b_page_count; i++)
- unlock_page(bp->b_pages[i]);
- }
-
- if (page_count == bp->b_page_count)
- bp->b_flags |= XBF_DONE;
-
+out_free_pages:
+ for (i = 0; i < bp->b_page_count; i++)
+ __free_page(bp->b_pages[i]);
return error;
}
@@ -450,8 +387,9 @@
xfs_buf_t *bp,
uint flags)
{
- /* A single page buffer is always mappable */
+ ASSERT(bp->b_flags & _XBF_PAGES);
if (bp->b_page_count == 1) {
+ /* A single page buffer is always mappable */
bp->b_addr = page_address(bp->b_pages[0]) + bp->b_offset;
bp->b_flags |= XBF_MAPPED;
} else if (flags & XBF_MAPPED) {
@@ -576,9 +514,14 @@
}
}
+ /*
+ * if the buffer is stale, clear all the external state associated with
+ * it. We need to keep flags such as how we allocated the buffer memory
+ * intact here.
+ */
if (bp->b_flags & XBF_STALE) {
ASSERT((bp->b_flags & _XBF_DELWRI_Q) == 0);
- bp->b_flags &= XBF_MAPPED;
+ bp->b_flags &= XBF_MAPPED | _XBF_KMEM | _XBF_PAGES;
}
trace_xfs_buf_find(bp, flags, _RET_IP_);
@@ -599,7 +542,7 @@
xfs_buf_flags_t flags)
{
xfs_buf_t *bp, *new_bp;
- int error = 0, i;
+ int error = 0;
new_bp = xfs_buf_allocate(flags);
if (unlikely(!new_bp))
@@ -607,7 +550,7 @@
bp = _xfs_buf_find(target, ioff, isize, flags, new_bp);
if (bp == new_bp) {
- error = _xfs_buf_lookup_pages(bp, flags);
+ error = xfs_buf_allocate_memory(bp, flags);
if (error)
goto no_buffer;
} else {
@@ -616,9 +559,6 @@
return NULL;
}
- for (i = 0; i < bp->b_page_count; i++)
- mark_page_accessed(bp->b_pages[i]);
-
if (!(bp->b_flags & XBF_MAPPED)) {
error = _xfs_buf_map_pages(bp, flags);
if (unlikely(error)) {
@@ -719,8 +659,7 @@
{
struct backing_dev_info *bdi;
- bdi = target->bt_mapping->backing_dev_info;
- if (bdi_read_congested(bdi))
+ if (bdi_read_congested(target->bt_bdi))
return;
xfs_buf_read(target, ioff, isize,
@@ -798,10 +737,10 @@
size_t buflen;
int page_count;
- pageaddr = (unsigned long)mem & PAGE_CACHE_MASK;
+ pageaddr = (unsigned long)mem & PAGE_MASK;
offset = (unsigned long)mem - pageaddr;
- buflen = PAGE_CACHE_ALIGN(len + offset);
- page_count = buflen >> PAGE_CACHE_SHIFT;
+ buflen = PAGE_ALIGN(len + offset);
+ page_count = buflen >> PAGE_SHIFT;
/* Free any previous set of page pointers */
if (bp->b_pages)
@@ -818,13 +757,12 @@
for (i = 0; i < bp->b_page_count; i++) {
bp->b_pages[i] = mem_to_page((void *)pageaddr);
- pageaddr += PAGE_CACHE_SIZE;
+ pageaddr += PAGE_SIZE;
}
bp->b_count_desired = len;
bp->b_buffer_length = buflen;
bp->b_flags |= XBF_MAPPED;
- bp->b_flags &= ~_XBF_PAGE_LOCKED;
return 0;
}
@@ -931,20 +869,7 @@
/*
- * Mutual exclusion on buffers. Locking model:
- *
- * Buffers associated with inodes for which buffer locking
- * is not enabled are not protected by semaphores, and are
- * assumed to be exclusively owned by the caller. There is a
- * spinlock in the buffer, used by the caller when concurrent
- * access is possible.
- */
-
-/*
- * Locks a buffer object, if it is not already locked. Note that this in
- * no way locks the underlying pages, so it is only useful for
- * synchronizing concurrent use of buffer objects, not for synchronizing
- * independent access to the underlying pages.
+ * Lock a buffer object, if it is not already locked.
*
* If we come across a stale, pinned, locked buffer, we know that we are
* being asked to lock a buffer that has been reallocated. Because it is
@@ -978,10 +903,7 @@
}
/*
- * Locks a buffer object.
- * Note that this in no way locks the underlying pages, so it is only
- * useful for synchronizing concurrent use of buffer objects, not for
- * synchronizing independent access to the underlying pages.
+ * Lock a buffer object.
*
* If we come across a stale, pinned, locked buffer, we know that we
* are being asked to lock a buffer that has been reallocated. Because
@@ -998,7 +920,7 @@
if (atomic_read(&bp->b_pin_count) && (bp->b_flags & XBF_STALE))
xfs_log_force(bp->b_target->bt_mount, 0);
if (atomic_read(&bp->b_io_remaining))
- blk_run_address_space(bp->b_target->bt_mapping);
+ blk_run_backing_dev(bp->b_target->bt_bdi, NULL);
down(&bp->b_sema);
XB_SET_OWNER(bp);
@@ -1043,7 +965,7 @@
if (atomic_read(&bp->b_pin_count) == 0)
break;
if (atomic_read(&bp->b_io_remaining))
- blk_run_address_space(bp->b_target->bt_mapping);
+ blk_run_backing_dev(bp->b_target->bt_bdi, NULL);
schedule();
}
remove_wait_queue(&bp->b_waiters, &wait);
@@ -1256,10 +1178,8 @@
xfs_buf_t *bp,
int schedule)
{
- if (atomic_dec_and_test(&bp->b_io_remaining) == 1) {
- bp->b_flags &= ~_XBF_PAGE_LOCKED;
+ if (atomic_dec_and_test(&bp->b_io_remaining) == 1)
xfs_buf_ioend(bp, schedule);
- }
}
STATIC void
@@ -1268,35 +1188,12 @@
int error)
{
xfs_buf_t *bp = (xfs_buf_t *)bio->bi_private;
- unsigned int blocksize = bp->b_target->bt_bsize;
- struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
xfs_buf_ioerror(bp, -error);
if (!error && xfs_buf_is_vmapped(bp) && (bp->b_flags & XBF_READ))
invalidate_kernel_vmap_range(bp->b_addr, xfs_buf_vmap_len(bp));
- do {
- struct page *page = bvec->bv_page;
-
- ASSERT(!PagePrivate(page));
- if (unlikely(bp->b_error)) {
- if (bp->b_flags & XBF_READ)
- ClearPageUptodate(page);
- } else if (blocksize >= PAGE_CACHE_SIZE) {
- SetPageUptodate(page);
- } else if (!PagePrivate(page) &&
- (bp->b_flags & _XBF_PAGE_CACHE)) {
- set_page_region(page, bvec->bv_offset, bvec->bv_len);
- }
-
- if (--bvec >= bio->bi_io_vec)
- prefetchw(&bvec->bv_page->flags);
-
- if (bp->b_flags & _XBF_PAGE_LOCKED)
- unlock_page(page);
- } while (bvec >= bio->bi_io_vec);
-
_xfs_buf_ioend(bp, 1);
bio_put(bio);
}
@@ -1310,7 +1207,6 @@
int offset = bp->b_offset;
int size = bp->b_count_desired;
sector_t sector = bp->b_bn;
- unsigned int blocksize = bp->b_target->bt_bsize;
total_nr_pages = bp->b_page_count;
map_i = 0;
@@ -1331,29 +1227,6 @@
(bp->b_flags & XBF_READ_AHEAD) ? READA : READ;
}
- /* Special code path for reading a sub page size buffer in --
- * we populate up the whole page, and hence the other metadata
- * in the same page. This optimization is only valid when the
- * filesystem block size is not smaller than the page size.
- */
- if ((bp->b_buffer_length < PAGE_CACHE_SIZE) &&
- ((bp->b_flags & (XBF_READ|_XBF_PAGE_LOCKED)) ==
- (XBF_READ|_XBF_PAGE_LOCKED)) &&
- (blocksize >= PAGE_CACHE_SIZE)) {
- bio = bio_alloc(GFP_NOIO, 1);
-
- bio->bi_bdev = bp->b_target->bt_bdev;
- bio->bi_sector = sector - (offset >> BBSHIFT);
- bio->bi_end_io = xfs_buf_bio_end_io;
- bio->bi_private = bp;
-
- bio_add_page(bio, bp->b_pages[0], PAGE_CACHE_SIZE, 0);
- size = 0;
-
- atomic_inc(&bp->b_io_remaining);
-
- goto submit_io;
- }
next_chunk:
atomic_inc(&bp->b_io_remaining);
@@ -1367,8 +1240,9 @@
bio->bi_end_io = xfs_buf_bio_end_io;
bio->bi_private = bp;
+
for (; size && nr_pages; nr_pages--, map_i++) {
- int rbytes, nbytes = PAGE_CACHE_SIZE - offset;
+ int rbytes, nbytes = PAGE_SIZE - offset;
if (nbytes > size)
nbytes = size;
@@ -1383,7 +1257,6 @@
total_nr_pages--;
}
-submit_io:
if (likely(bio->bi_size)) {
if (xfs_buf_is_vmapped(bp)) {
flush_kernel_vmap_range(bp->b_addr,
@@ -1393,18 +1266,7 @@
if (size)
goto next_chunk;
} else {
- /*
- * if we get here, no pages were added to the bio. However,
- * we can't just error out here - if the pages are locked then
- * we have to unlock them otherwise we can hang on a later
- * access to the page.
- */
xfs_buf_ioerror(bp, EIO);
- if (bp->b_flags & _XBF_PAGE_LOCKED) {
- int i;
- for (i = 0; i < bp->b_page_count; i++)
- unlock_page(bp->b_pages[i]);
- }
bio_put(bio);
}
}
@@ -1450,7 +1312,7 @@
trace_xfs_buf_iowait(bp, _RET_IP_);
if (atomic_read(&bp->b_io_remaining))
- blk_run_address_space(bp->b_target->bt_mapping);
+ blk_run_backing_dev(bp->b_target->bt_bdi, NULL);
wait_for_completion(&bp->b_iowait);
trace_xfs_buf_iowait_done(bp, _RET_IP_);
@@ -1468,8 +1330,8 @@
return XFS_BUF_PTR(bp) + offset;
offset += bp->b_offset;
- page = bp->b_pages[offset >> PAGE_CACHE_SHIFT];
- return (xfs_caddr_t)page_address(page) + (offset & (PAGE_CACHE_SIZE-1));
+ page = bp->b_pages[offset >> PAGE_SHIFT];
+ return (xfs_caddr_t)page_address(page) + (offset & (PAGE_SIZE-1));
}
/*
@@ -1491,9 +1353,9 @@
page = bp->b_pages[xfs_buf_btoct(boff + bp->b_offset)];
cpoff = xfs_buf_poff(boff + bp->b_offset);
csize = min_t(size_t,
- PAGE_CACHE_SIZE-cpoff, bp->b_count_desired-boff);
+ PAGE_SIZE-cpoff, bp->b_count_desired-boff);
- ASSERT(((csize + cpoff) <= PAGE_CACHE_SIZE));
+ ASSERT(((csize + cpoff) <= PAGE_SIZE));
switch (mode) {
case XBRW_ZERO:
@@ -1606,7 +1468,6 @@
xfs_flush_buftarg(btp, 1);
if (mp->m_flags & XFS_MOUNT_BARRIER)
xfs_blkdev_issue_flush(btp);
- iput(btp->bt_mapping->host);
kthread_stop(btp->bt_task);
kmem_free(btp);
@@ -1630,15 +1491,6 @@
return EINVAL;
}
- if (verbose &&
- (PAGE_CACHE_SIZE / BITS_PER_LONG) > sectorsize) {
- printk(KERN_WARNING
- "XFS: %u byte sectors in use on device %s. "
- "This is suboptimal; %u or greater is ideal.\n",
- sectorsize, XFS_BUFTARG_NAME(btp),
- (unsigned int)PAGE_CACHE_SIZE / BITS_PER_LONG);
- }
-
return 0;
}
@@ -1653,7 +1505,7 @@
struct block_device *bdev)
{
return xfs_setsize_buftarg_flags(btp,
- PAGE_CACHE_SIZE, bdev_logical_block_size(bdev), 0);
+ PAGE_SIZE, bdev_logical_block_size(bdev), 0);
}
int
@@ -1666,41 +1518,6 @@
}
STATIC int
-xfs_mapping_buftarg(
- xfs_buftarg_t *btp,
- struct block_device *bdev)
-{
- struct backing_dev_info *bdi;
- struct inode *inode;
- struct address_space *mapping;
- static const struct address_space_operations mapping_aops = {
- .sync_page = block_sync_page,
- .migratepage = fail_migrate_page,
- };
-
- inode = new_inode(bdev->bd_inode->i_sb);
- if (!inode) {
- printk(KERN_WARNING
- "XFS: Cannot allocate mapping inode for device %s\n",
- XFS_BUFTARG_NAME(btp));
- return ENOMEM;
- }
- inode->i_ino = get_next_ino();
- inode->i_mode = S_IFBLK;
- inode->i_bdev = bdev;
- inode->i_rdev = bdev->bd_dev;
- bdi = blk_get_backing_dev_info(bdev);
- if (!bdi)
- bdi = &default_backing_dev_info;
- mapping = &inode->i_data;
- mapping->a_ops = &mapping_aops;
- mapping->backing_dev_info = bdi;
- mapping_set_gfp_mask(mapping, GFP_NOFS);
- btp->bt_mapping = mapping;
- return 0;
-}
-
-STATIC int
xfs_alloc_delwrite_queue(
xfs_buftarg_t *btp,
const char *fsname)
@@ -1728,12 +1545,14 @@
btp->bt_mount = mp;
btp->bt_dev = bdev->bd_dev;
btp->bt_bdev = bdev;
+ btp->bt_bdi = blk_get_backing_dev_info(bdev);
+ if (!btp->bt_bdi)
+ goto error;
+
INIT_LIST_HEAD(&btp->bt_lru);
spin_lock_init(&btp->bt_lru_lock);
if (xfs_setsize_buftarg_early(btp, bdev))
goto error;
- if (xfs_mapping_buftarg(btp, bdev))
- goto error;
if (xfs_alloc_delwrite_queue(btp, fsname))
goto error;
btp->bt_shrinker.shrink = xfs_buftarg_shrink;
@@ -1955,7 +1774,7 @@
count++;
}
if (count)
- blk_run_address_space(target->bt_mapping);
+ blk_run_backing_dev(target->bt_bdi, NULL);
} while (!kthread_should_stop());
@@ -2003,7 +1822,7 @@
if (wait) {
/* Expedite and wait for IO to complete. */
- blk_run_address_space(target->bt_mapping);
+ blk_run_backing_dev(target->bt_bdi, NULL);
while (!list_empty(&wait_list)) {
bp = list_first_entry(&wait_list, struct xfs_buf, b_list);
