[PATCH] kill superflous buffer locking

Christoph Hellwig
2007-09-24T18:49:32Z

There is no need to lock any page in xfs_buf.c because we operate
on our own address_space and all locking is covered by the buffer
semaphore. If we ever switch back to main blockdeive address_space
as suggested e.g. for fsblock with a similar scheme the locking will
have to be totally revised anyway because the current scheme is
neither correct nor coherent with itself.

Signed-off-by: Christoph Hellwig <hch@lst.de>

Index: linux-2.6-xfs/fs/xfs/linux-2.6/xfs_buf.c
===================================================================
--- linux-2.6-xfs.orig/fs/xfs/linux-2.6/xfs_buf.c 2007-09-23 13:28:00.000000000 +0200
+++ linux-2.6-xfs/fs/xfs/linux-2.6/xfs_buf.c 2007-09-23 14:13:43.000000000 +0200
@@ -396,6 +396,7 @@ _xfs_buf_lookup_pages(
congestion_wait(WRITE, HZ/50);
goto retry;
}
+ unlock_page(page);

XFS_STATS_INC(xb_page_found);

@@ -405,10 +406,7 @@ _xfs_buf_lookup_pages(
ASSERT(!PagePrivate(page));
if (!PageUptodate(page)) {
page_count--;
- if (blocksize >= PAGE_CACHE_SIZE) {
- if (flags & XBF_READ)
- bp->b_locked = 1;
- } else if (!PagePrivate(page)) {
+ if (blocksize < PAGE_CACHE_SIZE && !PagePrivate(page)) {
if (test_page_region(page, offset, nbytes))
page_count++;
}
@@ -418,11 +416,6 @@ _xfs_buf_lookup_pages(
offset = 0;
}

- if (!bp->b_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;

@@ -747,7 +740,6 @@ xfs_buf_associate_memory(
bp->b_page_count = ++i;
ptr += PAGE_CACHE_SIZE;
}
- bp->b_locked = 0;

bp->b_count_desired = bp->b_buffer_length = len;
bp->b_flags |= XBF_MAPPED;
@@ -1093,25 +1085,13 @@ xfs_buf_iostart(
return status;
}

-STATIC_INLINE int
-_xfs_buf_iolocked(
- xfs_buf_t *bp)
-{
- ASSERT(bp->b_flags & (XBF_READ | XBF_WRITE));
- if (bp->b_flags & XBF_READ)
- return bp->b_locked;
- return 0;
-}
-
STATIC_INLINE void
_xfs_buf_ioend(
xfs_buf_t *bp,
int schedule)
{
- if (atomic_dec_and_test(&bp->b_io_remaining) == 1) {
- bp->b_locked = 0;
+ if (atomic_dec_and_test(&bp->b_io_remaining) == 1)
xfs_buf_ioend(bp, schedule);
- }
}

STATIC int
@@ -1146,10 +1126,6 @@ xfs_buf_bio_end_io(

if (--bvec >= bio->bi_io_vec)
prefetchw(&bvec->bv_page->flags);
-
- if (_xfs_buf_iolocked(bp)) {
- unlock_page(page);
- }
} while (bvec >= bio->bi_io_vec);

_xfs_buf_ioend(bp, 1);
@@ -1161,13 +1137,12 @@ STATIC void
_xfs_buf_ioapply(
xfs_buf_t *bp)
{
- int i, rw, map_i, total_nr_pages, nr_pages;
+ int rw, map_i, total_nr_pages, nr_pages;
struct bio *bio;
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;
- int locking = _xfs_buf_iolocked(bp);

total_nr_pages = bp->b_page_count;
map_i = 0;
@@ -1190,7 +1165,7 @@ _xfs_buf_ioapply(
* filesystem block size is not smaller than the page size.
*/
if ((bp->b_buffer_length < PAGE_CACHE_SIZE) &&
- (bp->b_flags & XBF_READ) && locking &&
+ (bp->b_flags & XBF_READ) &&
(blocksize >= PAGE_CACHE_SIZE)) {
bio = bio_alloc(GFP_NOIO, 1);

@@ -1207,24 +1182,6 @@ _xfs_buf_ioapply(
goto submit_io;
}

- /* Lock down the pages which we need to for the request */
- if (locking && (bp->b_flags & XBF_WRITE) && (bp->b_locked == 0)) {
- for (i = 0; size; i++) {
- int nbytes = PAGE_CACHE_SIZE - offset;
- struct page *page = bp->b_pages[i];
-
- if (nbytes > size)
- nbytes = size;
-
- lock_page(page);
-
- size -= nbytes;
- offset = 0;
- }
- offset = bp->b_offset;
- size = bp->b_count_desired;
- }
-
next_chunk:
atomic_inc(&bp->b_io_remaining);
nr_pages = BIO_MAX_SECTORS >> (PAGE_SHIFT - BBSHIFT);
Index: linux-2.6-xfs/fs/xfs/linux-2.6/xfs_buf.h
===================================================================
--- linux-2.6-xfs.orig/fs/xfs/linux-2.6/xfs_buf.h 2007-09-05 11:17:42.000000000 +0200
+++ linux-2.6-xfs/fs/xfs/linux-2.6/xfs_buf.h 2007-09-23 14:04:36.000000000 +0200
@@ -143,7 +143,6 @@ typedef struct xfs_buf {
void *b_fspriv2;
void *b_fspriv3;
unsigned short b_error; /* error code on I/O */
- unsigned short b_locked; /* page array is locked */
unsigned int b_page_count; /* size of page array */
unsigned int b_offset; /* page offset in first page */
struct page **b_pages; /* array of page pointers */
Index: linux-2.6-xfs/fs/xfs/xfsidbg.c
===================================================================
--- linux-2.6-xfs.orig/fs/xfs/xfsidbg.c 2007-09-23 13:33:07.000000000 +0200
+++ linux-2.6-xfs/fs/xfs/xfsidbg.c 2007-09-23 14:04:36.000000000 +0200
@@ -2110,9 +2110,9 @@ print_xfs_buf(
(unsigned long long) bp->b_file_offset,
(unsigned long long) bp->b_buffer_length,
bp->b_addr);
- kdb_printf(" b_bn 0x%llx b_count_desired 0x%lx b_locked %d\n",
+ kdb_printf(" b_bn 0x%llx b_count_desired 0x%lxn",
(unsigned long long)bp->b_bn,
- (unsigned long) bp->b_count_desired, (int)bp->b_locked);
+ (unsigned long) bp->b_count_desired);
kdb_printf(" b_queuetime %ld (now=%ld/age=%ld) b_io_remaining %d\n",
bp->b_queuetime, jiffies, bp->b_queuetime + age,
bp->b_io_remaining.counter);