Hi Jens,
What do you think of this patch? Can you possibly merge it via your
block tree if it looks OK?
Thanks,
Nick
--
brd: support discard
Support discard requests in brd by zeroing or deleting the underlying backing
pages. This is simply to help with testing and documentation nature of
brd code.
Signed-off-by: Nick Piggin <npiggin@xxxxxxx>
---
Index: linux-2.6/drivers/block/brd.c
===================================================================
--- linux-2.6.orig/drivers/block/brd.c
+++ linux-2.6/drivers/block/brd.c
@@ -133,6 +133,28 @@ static struct page *brd_insert_page(stru
return page;
}
+static void brd_free_page(struct brd_device *brd, sector_t sector)
+{
+ struct page *page;
+ pgoff_t idx;
+
+ spin_lock(&brd->brd_lock);
+ idx = sector >> PAGE_SECTORS_SHIFT;
+ page = radix_tree_delete(&brd->brd_pages, idx);
+ spin_unlock(&brd->brd_lock);
+ if (page)
+ __free_page(page);
+}
+
+static void brd_zero_page(struct brd_device *brd, sector_t sector)
+{
+ struct page *page;
+
+ page = brd_lookup_page(brd, sector);
+ if (page)
+ clear_highpage(page);
+}
+
/*
* Free all backing store pages and radix tree. This must only be called when
* there are no other users of the device.
@@ -189,6 +211,24 @@ static int copy_to_brd_setup(struct brd_
return 0;
}
+static void discard_from_brd(struct brd_device *brd,
+ sector_t sector, size_t n)
+{
+ while (n >= PAGE_SIZE) {
+ /*
+ * Don't want to actually discard pages here because
+ * re-allocating the pages can result in writeback
+ * deadlocks under heavy load.
+ */
+ if (0)
+ brd_free_page(brd, sector);
+ else
+ brd_zero_page(brd, sector);
+ sector += PAGE_SIZE >> SECTOR_SHIFT;
+ n -= PAGE_SIZE;
+ }
+}
+
/*
* Copy n bytes from src to the brd starting at sector. Does not sleep.
*/
@@ -300,6 +340,12 @@ static int brd_make_request(struct reque
get_capacity(bdev->bd_disk))
goto out;
+ if (unlikely(bio_rw_flagged(bio, BIO_RW_DISCARD))) {
+ err = 0;
+ discard_from_brd(brd, sector, bio->bi_size);
+ goto out;
+ }
+
rw = bio_rw(bio);
if (rw == READA)
rw = READ;
@@ -320,7 +366,7 @@ out:
}
#ifdef CONFIG_BLK_DEV_XIP
-static int brd_direct_access (struct block_device *bdev, sector_t sector,
+static int brd_direct_access(struct block_device *bdev, sector_t sector,
void **kaddr, unsigned long *pfn)
{
struct brd_device *brd = bdev->bd_disk->private_data;
@@ -437,6 +483,11 @@ static struct brd_device *brd_alloc(int
blk_queue_max_hw_sectors(brd->brd_queue, 1024);
blk_queue_bounce_limit(brd->brd_queue, BLK_BOUNCE_ANY);
+ brd->brd_queue->limits.discard_granularity = PAGE_SIZE;
+ brd->brd_queue->limits.max_discard_sectors = UINT_MAX;
+ brd->brd_queue->limits.discard_zeroes_data = 1;
+ queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, brd->brd_queue);
+
disk = brd->brd_disk = alloc_disk(1 << part_shift);
if (!disk)
goto out_free_queue;
--
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