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authorJosef Bacik <josef@redhat.com>2011-09-30 15:23:54 -0400
committerChris Mason <chris.mason@oracle.com>2011-09-30 15:23:54 -0400
commitb6316429af7f365f307dfd2b6a7a42f2563aef19 (patch)
treef445576e448d3287d56650775bb7d0bc5a7d37c7
parentb6f3409b2197e8fcedb43e6600e37b7cfbe0715b (diff)
Btrfs: force a page fault if we have a shorty copy on a page boundary
A user reported a problem where ceph was getting into 100% cpu usage while doing some writing. It turns out it's because we were doing a short write on a not uptodate page, which means we'd fall back at one page at a time and fault the page in. The problem is our position is on the page boundary, so our fault in logic wasn't actually reading the page, so we'd just spin forever or until the page got read in by somebody else. This will force a readpage if we end up doing a short copy. Alexandre could reproduce this easily with ceph and reports it fixes his problem. I also wrote a reproducer that no longer hangs my box with this patch. Thanks, Reported-and-tested-by: Alexandre Oliva <aoliva@redhat.com> Signed-off-by: Josef Bacik <josef@redhat.com> Signed-off-by: Chris Mason <chris.mason@oracle.com>
-rw-r--r--fs/btrfs/file.c24
1 files changed, 16 insertions, 8 deletions
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 98d95bb5f253..e73051099368 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1036,11 +1036,13 @@ out:
* on error we return an unlocked page and the error value
* on success we return a locked page and 0
*/
-static int prepare_uptodate_page(struct page *page, u64 pos)
+static int prepare_uptodate_page(struct page *page, u64 pos,
+ bool force_uptodate)
{
int ret = 0;
- if ((pos & (PAGE_CACHE_SIZE - 1)) && !PageUptodate(page)) {
+ if (((pos & (PAGE_CACHE_SIZE - 1)) || force_uptodate) &&
+ !PageUptodate(page)) {
ret = btrfs_readpage(NULL, page);
if (ret)
return ret;
@@ -1061,7 +1063,7 @@ static int prepare_uptodate_page(struct page *page, u64 pos)
static noinline int prepare_pages(struct btrfs_root *root, struct file *file,
struct page **pages, size_t num_pages,
loff_t pos, unsigned long first_index,
- size_t write_bytes)
+ size_t write_bytes, bool force_uptodate)
{
struct extent_state *cached_state = NULL;
int i;
@@ -1086,10 +1088,11 @@ again:
}
if (i == 0)
- err = prepare_uptodate_page(pages[i], pos);
+ err = prepare_uptodate_page(pages[i], pos,
+ force_uptodate);
if (i == num_pages - 1)
err = prepare_uptodate_page(pages[i],
- pos + write_bytes);
+ pos + write_bytes, false);
if (err) {
page_cache_release(pages[i]);
faili = i - 1;
@@ -1158,6 +1161,7 @@ static noinline ssize_t __btrfs_buffered_write(struct file *file,
size_t num_written = 0;
int nrptrs;
int ret = 0;
+ bool force_page_uptodate = false;
nrptrs = min((iov_iter_count(i) + PAGE_CACHE_SIZE - 1) /
PAGE_CACHE_SIZE, PAGE_CACHE_SIZE /
@@ -1200,7 +1204,8 @@ static noinline ssize_t __btrfs_buffered_write(struct file *file,
* contents of pages from loop to loop
*/
ret = prepare_pages(root, file, pages, num_pages,
- pos, first_index, write_bytes);
+ pos, first_index, write_bytes,
+ force_page_uptodate);
if (ret) {
btrfs_delalloc_release_space(inode,
num_pages << PAGE_CACHE_SHIFT);
@@ -1217,12 +1222,15 @@ static noinline ssize_t __btrfs_buffered_write(struct file *file,
if (copied < write_bytes)
nrptrs = 1;
- if (copied == 0)
+ if (copied == 0) {
+ force_page_uptodate = true;
dirty_pages = 0;
- else
+ } else {
+ force_page_uptodate = false;
dirty_pages = (copied + offset +
PAGE_CACHE_SIZE - 1) >>
PAGE_CACHE_SHIFT;
+ }
/*
* If we had a short copy we need to release the excess delaloc