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Message-ID: <20110912134202.GA22953@infradead.org>
Date: Mon, 12 Sep 2011 09:42:02 -0400
From: Christoph Hellwig <hch@...radead.org>
To: Jens Axboe <axboe@...nel.dk>
Cc: linux-raid@...r.kernel.org, dm-devel@...hat.com,
linux-kernel@...r.kernel.org
Subject: [PATCH 3/2] block: refactor generic_make_request
Move all the checks performed on a bio into a new helper, and call it as
soon as bio is submitted even if it is a re-submission from ->make_request.
We explicitly mark the new helper as beeing non-inlined as the stack
usage for printing the block device name in the failure case is quite
high and this a patch where we have to be extremely conservative about
stack usage.
Signed-off-by: Christoph Hellwig <hch@....de>
Index: linux-2.6/block/blk-core.c
===================================================================
--- linux-2.6.orig/block/blk-core.c 2011-09-08 12:07:09.943065855 +0200
+++ linux-2.6/block/blk-core.c 2011-09-08 12:08:23.463277870 +0200
@@ -1412,31 +1412,8 @@ static inline int bio_check_eod(struct b
return 0;
}
-/**
- * generic_make_request - hand a buffer to its device driver for I/O
- * @bio: The bio describing the location in memory and on the device.
- *
- * generic_make_request() is used to make I/O requests of block
- * devices. It is passed a &struct bio, which describes the I/O that needs
- * to be done.
- *
- * generic_make_request() does not return any status. The
- * success/failure status of the request, along with notification of
- * completion, is delivered asynchronously through the bio->bi_end_io
- * function described (one day) else where.
- *
- * The caller of generic_make_request must make sure that bi_io_vec
- * are set to describe the memory buffer, and that bi_dev and bi_sector are
- * set to describe the device address, and the
- * bi_end_io and optionally bi_private are set to describe how
- * completion notification should be signaled.
- *
- * generic_make_request and the drivers it calls may use bi_next if this
- * bio happens to be merged with someone else, and may change bi_dev and
- * bi_sector for remaps as it sees fit. So the values of these fields
- * should NOT be depended on after the call to generic_make_request.
- */
-static inline void __generic_make_request(struct bio *bio)
+static noinline_for_stack bool
+generic_make_request_checks(struct bio *bio)
{
struct request_queue *q;
int nr_sectors = bio_sectors(bio);
@@ -1515,35 +1492,62 @@ static inline void __generic_make_reques
/* if bio = NULL, bio has been throttled and will be submitted later. */
if (!bio)
- return;
+ return false;
+
trace_block_bio_queue(q, bio);
- q->make_request_fn(q, bio);
- return;
+ return true;
end_io:
bio_endio(bio, err);
+ return false;
}
-/*
- * We only want one ->make_request_fn to be active at a time,
- * else stack usage with stacked devices could be a problem.
- * So use current->bio_list to keep a list of requests
- * submited by a make_request_fn function.
- * current->bio_list is also used as a flag to say if
- * generic_make_request is currently active in this task or not.
- * If it is NULL, then no make_request is active. If it is non-NULL,
- * then a make_request is active, and new requests should be added
- * at the tail
+/**
+ * generic_make_request - hand a buffer to its device driver for I/O
+ * @bio: The bio describing the location in memory and on the device.
+ *
+ * generic_make_request() is used to make I/O requests of block
+ * devices. It is passed a &struct bio, which describes the I/O that needs
+ * to be done.
+ *
+ * generic_make_request() does not return any status. The
+ * success/failure status of the request, along with notification of
+ * completion, is delivered asynchronously through the bio->bi_end_io
+ * function described (one day) else where.
+ *
+ * The caller of generic_make_request must make sure that bi_io_vec
+ * are set to describe the memory buffer, and that bi_dev and bi_sector are
+ * set to describe the device address, and the
+ * bi_end_io and optionally bi_private are set to describe how
+ * completion notification should be signaled.
+ *
+ * generic_make_request and the drivers it calls may use bi_next if this
+ * bio happens to be merged with someone else, and may resubmit the bio to
+ * a lower device by calling into generic_make_request recursively, which
+ * means the bio should NOT be touched after the call to ->make_request_fn.
*/
void generic_make_request(struct bio *bio)
{
struct bio_list bio_list_on_stack;
+ if (!generic_make_request_checks(bio))
+ return;
+
+ /*
+ * We only want one ->make_request_fn to be active at a time, else
+ * stack usage with stacked devices could be a problem. So use
+ * current->bio_list to keep a list of requests submited by a
+ * make_request_fn function. current->bio_list is also used as a
+ * flag to say if generic_make_request is currently active in this
+ * task or not. If it is NULL, then no make_request is active. If
+ * it is non-NULL, then a make_request is active, and new requests
+ * should be added at the tail
+ */
if (current->bio_list) {
- /* make_request is active */
bio_list_add(current->bio_list, bio);
return;
}
+
/* following loop may be a bit non-obvious, and so deserves some
* explanation.
* Before entering the loop, bio->bi_next is NULL (as all callers
@@ -1557,16 +1561,15 @@ void generic_make_request(struct bio *bi
* from the top. In this case we really did just take the bio
* of the top of the list (no pretending) and so remove it from
* bio_list, and call into __generic_make_request again.
- *
- * The loop was structured like this to make only one call to
- * __generic_make_request (which is important as it is large and
- * inlined) and to keep the structure simple.
*/
BUG_ON(bio->bi_next);
bio_list_init(&bio_list_on_stack);
current->bio_list = &bio_list_on_stack;
do {
- __generic_make_request(bio);
+ struct request_queue *q = bdev_get_queue(bio->bi_bdev);
+
+ q->make_request_fn(q, bio);
+
bio = bio_list_pop(current->bio_list);
} while (bio);
current->bio_list = NULL; /* deactivate */
--
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