From: Suparna Bhattacharya <suparna@in.ibm.com>
From: Andrew Morton <akpm@osdl.org>
Modify mpage_writepages to optionally only write back dirty pages within a
specified range in a file (as in the case of O_SYNC). Cheat a little to avoid
changes to prototypes of aops - just put the <start, end> hint into the
writeback_control struct instead. If <start, end> are not set, then default
to writing back all the mapping's dirty pages.
Signed-off-by: Suparna Bhattacharya <suparna@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-akpm/fs/mpage.c | 27 ++++++++++++++++++++++++---
25-akpm/include/linux/writeback.h | 21 ++++++++++++++++-----
2 files changed, 40 insertions(+), 8 deletions(-)
diff -puN fs/mpage.c~writeback-page-range-hint fs/mpage.c
--- 25/fs/mpage.c~writeback-page-range-hint 2004-08-01 17:23:55.316030856 -0700
+++ 25-akpm/fs/mpage.c 2004-08-01 17:23:55.322029944 -0700
@@ -627,7 +627,9 @@ mpage_writepages(struct address_space *m
struct pagevec pvec;
int nr_pages;
pgoff_t index;
+ pgoff_t end = -1; /* Inclusive */
int scanned = 0;
+ int is_range = 0;
if (wbc->nonblocking && bdi_write_congested(bdi)) {
wbc->encountered_congestion = 1;
@@ -645,9 +647,16 @@ mpage_writepages(struct address_space *m
index = 0; /* whole-file sweep */
scanned = 1;
}
+ if (wbc->start || wbc->end) {
+ index = wbc->start >> PAGE_CACHE_SHIFT;
+ end = wbc->end >> PAGE_CACHE_SHIFT;
+ is_range = 1;
+ scanned = 1;
+ }
retry:
while (!done && (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
- PAGECACHE_TAG_DIRTY, PAGEVEC_SIZE))) {
+ PAGECACHE_TAG_DIRTY,
+ min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) {
unsigned i;
scanned = 1;
@@ -664,10 +673,21 @@ retry:
lock_page(page);
+ if (unlikely(page->mapping != mapping)) {
+ unlock_page(page);
+ continue;
+ }
+
+ if (unlikely(is_range) && page->index > end) {
+ done = 1;
+ unlock_page(page);
+ continue;
+ }
+
if (wbc->sync_mode != WB_SYNC_NONE)
wait_on_page_writeback(page);
- if (page->mapping != mapping || PageWriteback(page) ||
+ if (PageWriteback(page) ||
!clear_page_dirty_for_io(page)) {
unlock_page(page);
continue;
@@ -706,7 +726,8 @@ retry:
index = 0;
goto retry;
}
- mapping->writeback_index = index;
+ if (!is_range)
+ mapping->writeback_index = index;
if (bio)
mpage_bio_submit(WRITE, bio);
return ret;
diff -puN include/linux/writeback.h~writeback-page-range-hint include/linux/writeback.h
--- 25/include/linux/writeback.h~writeback-page-range-hint 2004-08-01 17:23:55.317030704 -0700
+++ 25-akpm/include/linux/writeback.h 2004-08-01 17:23:55.323029792 -0700
@@ -29,7 +29,9 @@ enum writeback_sync_modes {
};
/*
- * A control structure which tells the writeback code what to do
+ * A control structure which tells the writeback code what to do. These are
+ * always on the stack, and hence need no locking. They are always initialised
+ * in a manner such that unspecified fields are set to zero.
*/
struct writeback_control {
struct backing_dev_info *bdi; /* If !NULL, only write back this
@@ -40,10 +42,19 @@ struct writeback_control {
long nr_to_write; /* Write this many pages, and decrement
this for each page written */
long pages_skipped; /* Pages which were not written */
- int nonblocking; /* Don't get stuck on request queues */
- int encountered_congestion; /* An output: a queue is full */
- int for_kupdate; /* A kupdate writeback */
- int for_reclaim; /* Invoked from the page allocator */
+
+ /*
+ * For a_ops->writepages(): is start or end are non-zero then this is
+ * a hint that the filesystem need only write out the pages inside that
+ * byterange. The byte at `end' is included in the writeout request.
+ */
+ loff_t start;
+ loff_t end;
+
+ int nonblocking:1; /* Don't get stuck on request queues */
+ int encountered_congestion:1; /* An output: a queue is full */
+ int for_kupdate:1; /* A kupdate writeback */
+ int for_reclaim:1; /* Invoked from the page allocator */
};
/*
_