On Fri, Nov 07, 2014 at 12:08:14AM -0500, Martin K. Petersen wrote: > blkdev_issue_discard() will zero a given block range on disk. This is > done by way of either WRITE SAME or regular WRITE. I.e. the blocks on > disk will be written and thus provisioned. > > There are use cases where the desired behavior is to zero the blocks but > unprovision them if possible. The blocks must deterministically contain > zeroes when they are subsequently read back. > > This patch introduces a blkdev_issue_zeroout_discard() call that > provides this functionality. If a block device guarantees > discard_zeroes_data the new function will use discard to clear the block > range. If the device does not support discard_zeroes_data or if the > discard request fails we will fall back to blkdev_issue_zeroout() to > ensure predictable results. Can this be plumbed into a BLK* ioctl too? I'll write a patch, if this is ok with everyone: struct blkzeroout_t { __u64 start; __u64 end; __u32 flags; }; #define BLKZEROOUT_DISCARD_OK 1 #define BLKZEROOUT_V2 _IOR(0x12, 127, sizeof(struct blkzeroout_t)) ...and make it zap the page cache per earlier discussion. This seems to be a good fit with what we've been discussing for mke2fs. --D > > Signed-off-by: Martin K. Petersen <martin.petersen@xxxxxxxxxx> > --- > block/blk-lib.c | 44 ++++++++++++++++++++++++++++++++++++++++++-- > include/linux/blkdev.h | 2 ++ > 2 files changed, 44 insertions(+), 2 deletions(-) > > diff --git a/block/blk-lib.c b/block/blk-lib.c > index 8411be3c19d3..2ffec6a01c71 100644 > --- a/block/blk-lib.c > +++ b/block/blk-lib.c > @@ -278,14 +278,18 @@ static int __blkdev_issue_zeroout(struct block_device *bdev, sector_t sector, > } > > /** > - * blkdev_issue_zeroout - zero-fill a block range > + * blkdev_issue_zeroout - zero-fill and provision a block range > * @bdev: blockdev to write > * @sector: start sector > * @nr_sects: number of sectors to write > * @gfp_mask: memory allocation flags (for bio_alloc) > * > * Description: > - * Generate and issue number of bios with zerofiled pages. > + * Zero-fill a block range. The blocks will be provisioned > + * (allocated/anchored) and are guaranteed to return zeroes when read > + * back. This function will attempt to use WRITE SAME to optimize the > + * process if the block device supports it. Otherwise it will fall back > + * to zeroing the blocks using regular WRITE calls. > */ > > int blkdev_issue_zeroout(struct block_device *bdev, sector_t sector, > @@ -305,3 +309,39 @@ int blkdev_issue_zeroout(struct block_device *bdev, sector_t sector, > return __blkdev_issue_zeroout(bdev, sector, nr_sects, gfp_mask); > } > EXPORT_SYMBOL(blkdev_issue_zeroout); > + > +/** > + * blkdev_issue_zeroout_discard - zero-fill and attempt to discard block range > + * @bdev: blockdev to write > + * @sector: start sector > + * @nr_sects: number of sectors to write > + * @gfp_mask: memory allocation flags (for bio_alloc) > + * > + * Description: > + * Zero-fill a block range. In contrast to blkdev_issue_zeroout() this > + * function will attempt to deprovision (deallocate/discard) the blocks > + * in question. It will only do so if the underlying device guarantees > + * that subsequent READ operations to the block range in question will > + * return zeroes. If the device does not provide hard guarantees or if > + * the DISCARD attempt should fail the block range will be explicitly > + * zeroed using blkdev_issue_zeroout(). > + */ > + > +int blkdev_issue_zeroout_discard(struct block_device *bdev, sector_t sector, > + sector_t nr_sects, gfp_t gfp_mask) > +{ > + struct request_queue *q = bdev_get_queue(bdev); > + > + if (blk_queue_discard(q) && q->limits.discard_zeroes_data) { > + unsigned char bdn[BDEVNAME_SIZE]; > + > + if (!blkdev_issue_discard(bdev, sector, nr_sects, gfp_mask, 0)) > + return 0; > + > + bdevname(bdev, bdn); > + pr_err("%s: DISCARD failed. Manually zeroing.\n", bdn); > + } > + > + return blkdev_issue_zeroout(bdev, sector, nr_sects, gfp_mask); > +} > +EXPORT_SYMBOL(blkdev_issue_zeroout_discard); > diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h > index aac0f9ea952a..078b6e5f488a 100644 > --- a/include/linux/blkdev.h > +++ b/include/linux/blkdev.h > @@ -1164,6 +1164,8 @@ extern int blkdev_issue_write_same(struct block_device *bdev, sector_t sector, > sector_t nr_sects, gfp_t gfp_mask, struct page *page); > extern int blkdev_issue_zeroout(struct block_device *bdev, sector_t sector, > sector_t nr_sects, gfp_t gfp_mask); > +extern int blkdev_issue_zeroout_discard(struct block_device *bdev, > + sector_t sector, sector_t nr_sects, gfp_t gfp_mask); > static inline int sb_issue_discard(struct super_block *sb, sector_t block, > sector_t nr_blocks, gfp_t gfp_mask, unsigned long flags) > { > -- > 1.9.3 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html