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Subject[PATCH] 2.6.8-rc4-mm1 DIO pages-in-io accounting fix
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Hi Andrew,

I found one more accounting inconsistency with dio_pages_in_io.
This is a day-one bug and I started hitting it on latest -mm
due to the recent changes to dio_pages_in_io calculations to be
exact.

If the file is badly fragmented (no contiguous blocks at all),
and the user buffer is not page aligned - we need to create
IO for each disk block with 2 pages. (bio with 2 vecs).

dio_bio_add_page() should not decrement dio_pages_in_io for every
add page. It should only decrement, it only if its done with that
page and moving on to next page. (since dio_pages_in_io represent
how many actual pages we are operating on).

Here is the patch to fix this accounting. Without this patch, we
will hit BUG() in dio_new_bio() with O_DIRECT on filesystems,.

Thanks,
Badari


--- linux.org/fs/direct-io.c 2004-08-16 10:57:33.112528208 -0700
+++ linux-2.6.8-rc4-mm1/fs/direct-io.c 2004-08-16 10:59:10.668697416 -0700
@@ -561,7 +561,11 @@ static int dio_bio_add_page(struct dio *
ret = bio_add_page(dio->bio, dio->cur_page,
dio->cur_page_len, dio->cur_page_offset);
if (ret == dio->cur_page_len) {
- dio->pages_in_io--;
+ /*
+ * Decrement count only, if we are done with this page
+ */
+ if ((dio->cur_page_len + dio->cur_page_offset) == PAGE_SIZE)
+ dio->pages_in_io--;
page_cache_get(dio->cur_page);
dio->final_block_in_bio = dio->cur_page_block +
(dio->cur_page_len >> dio->blkbits);
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