[PATCH, RFC] block: don't allocate a payload for discard request
From: Christoph Hellwig
Date: Fri Jun 18 2010 - 11:00:13 EST
Allocating a fixed payload for discard requests always was a horrible hack,
and it's not coming to byte us when adding support for discard in DM/MD.
So change the code to leave the allocation of a payload to the lowlevel
driver. Unfortunately that means we'll need another hack, which allows
us to update the various block layer length fields indicating that we
have a payload. Instead of hiding this in sd.c, which we already partially
do for UNMAP support add a documented helper in the core block layer for it.
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Index: linux-2.6/block/blk-lib.c
===================================================================
--- linux-2.6.orig/block/blk-lib.c 2010-06-18 11:33:37.313260457 +0200
+++ linux-2.6/block/blk-lib.c 2010-06-18 16:49:20.854319055 +0200
@@ -19,7 +19,6 @@ static void blkdev_discard_end_io(struct
if (bio->bi_private)
complete(bio->bi_private);
- __free_page(bio_page(bio));
bio_put(bio);
}
@@ -43,7 +42,6 @@ int blkdev_issue_discard(struct block_de
int type = flags & BLKDEV_IFL_BARRIER ?
DISCARD_BARRIER : DISCARD_NOBARRIER;
struct bio *bio;
- struct page *page;
int ret = 0;
if (!q)
@@ -53,35 +51,21 @@ int blkdev_issue_discard(struct block_de
return -EOPNOTSUPP;
while (nr_sects && !ret) {
- unsigned int sector_size = q->limits.logical_block_size;
unsigned int max_discard_sectors =
min(q->limits.max_discard_sectors, UINT_MAX >> 9);
bio = bio_alloc(gfp_mask, 1);
- if (!bio)
- goto out;
+ if (!bio) {
+ ret = -ENOMEM;
+ break;
+ }
+
bio->bi_sector = sector;
bio->bi_end_io = blkdev_discard_end_io;
bio->bi_bdev = bdev;
if (flags & BLKDEV_IFL_WAIT)
bio->bi_private = &wait;
- /*
- * Add a zeroed one-sector payload as that's what
- * our current implementations need. If we'll ever need
- * more the interface will need revisiting.
- */
- page = alloc_page(gfp_mask | __GFP_ZERO);
- if (!page)
- goto out_free_bio;
- if (bio_add_pc_page(q, bio, page, sector_size, 0) < sector_size)
- goto out_free_page;
-
- /*
- * And override the bio size - the way discard works we
- * touch many more blocks on disk than the actual payload
- * length.
- */
if (nr_sects > max_discard_sectors) {
bio->bi_size = max_discard_sectors << 9;
nr_sects -= max_discard_sectors;
@@ -103,13 +87,8 @@ int blkdev_issue_discard(struct block_de
ret = -EIO;
bio_put(bio);
}
+
return ret;
-out_free_page:
- __free_page(page);
-out_free_bio:
- bio_put(bio);
-out:
- return -ENOMEM;
}
EXPORT_SYMBOL(blkdev_issue_discard);
Index: linux-2.6/drivers/scsi/sd.c
===================================================================
--- linux-2.6.orig/drivers/scsi/sd.c 2010-06-18 11:33:37.322253892 +0200
+++ linux-2.6/drivers/scsi/sd.c 2010-06-18 16:50:04.790255778 +0200
@@ -411,22 +411,25 @@ static void sd_prot_op(struct scsi_cmnd
}
/**
- * sd_prepare_discard - unmap blocks on thinly provisioned device
+ * scsi_setup_discard_cmnd - unmap blocks on thinly provisioned device
+ * @sdp: scsi device to operate one
* @rq: Request to prepare
*
* Will issue either UNMAP or WRITE SAME(16) depending on preference
* indicated by target device.
**/
-static int sd_prepare_discard(struct request *rq)
+static int scsi_setup_discard_cmnd(struct scsi_device *sdp, struct request *rq)
{
struct scsi_disk *sdkp = scsi_disk(rq->rq_disk);
struct bio *bio = rq->bio;
sector_t sector = bio->bi_sector;
- unsigned int num = bio_sectors(bio);
+ unsigned int nr_sectors = bio_sectors(bio);
+ unsigned int len;
+ struct page *page;
if (sdkp->device->sector_size == 4096) {
sector >>= 3;
- num >>= 3;
+ nr_sectors >>= 3;
}
rq->cmd_type = REQ_TYPE_BLOCK_PC;
@@ -434,31 +437,35 @@ static int sd_prepare_discard(struct req
memset(rq->cmd, 0, rq->cmd_len);
+ page = alloc_page(GFP_ATOMIC | __GFP_ZERO);
+ if (!page)
+ return BLKPREP_DEFER;
+
if (sdkp->unmap) {
- char *buf = kmap_atomic(bio_page(bio), KM_USER0);
+ char *buf = page_address(page);
+ rq->cmd_len = 10;
rq->cmd[0] = UNMAP;
rq->cmd[8] = 24;
- rq->cmd_len = 10;
-
- /* Ensure that data length matches payload */
- rq->__data_len = bio->bi_size = bio->bi_io_vec->bv_len = 24;
put_unaligned_be16(6 + 16, &buf[0]);
put_unaligned_be16(16, &buf[2]);
put_unaligned_be64(sector, &buf[8]);
- put_unaligned_be32(num, &buf[16]);
+ put_unaligned_be32(nr_sectors, &buf[16]);
- kunmap_atomic(buf, KM_USER0);
+ len = 24;
} else {
+ rq->cmd_len = 16;
rq->cmd[0] = WRITE_SAME_16;
rq->cmd[1] = 0x8; /* UNMAP */
put_unaligned_be64(sector, &rq->cmd[2]);
- put_unaligned_be32(num, &rq->cmd[10]);
- rq->cmd_len = 16;
+ put_unaligned_be32(nr_sectors, &rq->cmd[10]);
+
+ len = sdkp->device->sector_size;
}
- return BLKPREP_OK;
+ blk_add_request_payload(rq, page, len);
+ return scsi_setup_blk_pc_cmnd(sdp, rq);
}
/**
@@ -485,10 +492,10 @@ static int sd_prep_fn(struct request_que
* Discard request come in as REQ_TYPE_FS but we turn them into
* block PC requests to make life easier.
*/
- if (rq->cmd_flags & REQ_DISCARD)
- ret = sd_prepare_discard(rq);
-
- if (rq->cmd_type == REQ_TYPE_BLOCK_PC) {
+ if (rq->cmd_flags & REQ_DISCARD) {
+ ret = scsi_setup_discard_cmnd(sdp, rq);
+ goto out;
+ } else if (rq->cmd_type == REQ_TYPE_BLOCK_PC) {
ret = scsi_setup_blk_pc_cmnd(sdp, rq);
goto out;
} else if (rq->cmd_type != REQ_TYPE_FS) {
@@ -1163,6 +1170,15 @@ static int sd_done(struct scsi_cmnd *SCp
int sense_valid = 0;
int sense_deferred = 0;
+ /*
+ * If this is a discard request that originated from the kernel
+ * we need to free our payload here. Note that we need to check
+ * the request flag as the normal payload rules apply for
+ * pass-through UNMAP / WRITE SAME requests.
+ */
+ if (SCpnt->request->cmd_flags & REQ_DISCARD)
+ __free_page(bio_page(SCpnt->request->bio));
+
if (result) {
sense_valid = scsi_command_normalize_sense(SCpnt, &sshdr);
if (sense_valid)
Index: linux-2.6/block/blk-core.c
===================================================================
--- linux-2.6.orig/block/blk-core.c 2010-06-18 16:43:23.711273168 +0200
+++ linux-2.6/block/blk-core.c 2010-06-18 16:48:17.392256056 +0200
@@ -1135,6 +1135,38 @@ void blk_put_request(struct request *req
}
EXPORT_SYMBOL(blk_put_request);
+/**
+ * blk_add_request_payload - add a payload to a request
+ * @rq: request to update
+ * @page: page backing the payload
+ * @len: length of the payload.
+ *
+ * This allows to later add a payload to an already submitted request by
+ * a block driver. The driver needs to take care of freeing the payload
+ * itself.
+ *
+ * Note that this is a quite horrible hack and nothing but handling of
+ * discard requests should ever use it.
+ */
+void blk_add_request_payload(struct request *rq, struct page *page,
+ unsigned int len)
+{
+ struct bio *bio = rq->bio;
+
+ bio->bi_io_vec->bv_page = page;
+ bio->bi_io_vec->bv_offset = 0;
+ bio->bi_io_vec->bv_len = len;
+
+ bio->bi_size = len;
+ bio->bi_vcnt = 1;
+ bio->bi_phys_segments = 1;
+
+ rq->__data_len = rq->resid_len = len;
+ rq->nr_phys_segments = 1;
+ rq->buffer = bio_data(bio);
+}
+EXPORT_SYMBOL_GPL(blk_add_request_payload);
+
void init_request_from_bio(struct request *req, struct bio *bio)
{
req->cpu = bio->bi_comp_cpu;
Index: linux-2.6/include/linux/blkdev.h
===================================================================
--- linux-2.6.orig/include/linux/blkdev.h 2010-06-18 16:45:29.223003718 +0200
+++ linux-2.6/include/linux/blkdev.h 2010-06-18 16:47:25.894005813 +0200
@@ -702,6 +702,8 @@ extern struct request *blk_make_request(
gfp_t);
extern void blk_insert_request(struct request_queue *, struct request *, int, void *);
extern void blk_requeue_request(struct request_queue *, struct request *);
+extern void blk_add_request_payload(struct request *rq, struct page *page,
+ unsigned int len);
extern int blk_rq_check_limits(struct request_queue *q, struct request *rq);
extern int blk_lld_busy(struct request_queue *q);
extern int blk_rq_prep_clone(struct request *rq, struct request *rq_src,
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/