From: Tao Ma on
Hi Andrew,
> Yes, that's a buglet.
> Note that Christoph's "[PATCH, RFC] block: don't allocate a payload for
> discard request" will fix it in a better way. That patch is in
> linux-next now, but I expect it will be taken out again (quickly,
> please) because Mike has found a number of problems with it.
ok, I haven't noticed that. thanks for the info.
> Your patch looks like a decent temporary fix for mainline, and a
> permanent one for -stable.
I am sorry, but I made a mistake. BIO_RW_DISCARD is a enum for bit offset.
So the right check should be rw & (1 << BIO_RW_DISCARD).
I have regenerated the patch. Sorry for the inconvenience.


From 060630d842a987a518c648ff65160639100c9a1b Mon Sep 17 00:00:00 2001
From: Tao Ma <>
Date: Thu, 24 Jun 2010 07:43:57 +0800
Subject: [PATCH v2] block: Don't count_vm_events for discard bio in submit_bio.

In submit_bio, we count vm events by check READ/WRITE.
But actually DISCARD_NOBARRIER also has the WRITE flag set.
It looks as if in blkdev_issue_discard, we also add a
page as the payload and the bio_has_data check isn't enough.
So add another check for discard bio.

Signed-off-by: Tao Ma <>
block/blk-core.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index f84cce4..26aa542 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1586,7 +1586,7 @@ void submit_bio(int rw, struct bio *bio)
* If it's a regular read/write or a barrier with data attached,
* go through the normal accounting stuff before submission.
- if (bio_has_data(bio)) {
+ if (bio_has_data(bio) && !(rw & (1 << BIO_RW_DISCARD))) {
if (rw & WRITE) {
count_vm_events(PGPGOUT, count);
} else {

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