On Thu, 13 Mar 2014 11:46:17 +0900 Joonsoo Kim <iamjoonsoo....@lge.com> wrote:
> Hello, Andrew.
>
> I applied all your comments in below patch. :)
OK, thanks. I'll grab this instead of v5 - I wasn't thinking very
clearly with the lock hold time issue. Let's go for low latency then
worry about it later if this function starts showing on profiles.
I modified your code comments somewhat - please check.
--- a/drivers/block/zram/zram_drv.c~zram-support-req_discard-v4-fix
+++ a/drivers/block/zram/zram_drv.c
@@ -552,8 +552,8 @@ static int zram_bvec_rw(struct zram *zra
/*
* zram_bio_discard - handler on discard request
- * @index: physical block index by PAGE_SIZE unit
- * @offset: offset within physical block
+ * @index: physical block index in PAGE_SIZE units
+ * @offset: byte offset within physical block
*/
static void zram_bio_discard(struct zram *zram, u32 index,
int offset, struct bio *bio)
@@ -561,14 +561,14 @@ static void zram_bio_discard(struct zram
size_t n = bio->bi_iter.bi_size;
/*
- * zram manages data by physical block size unit. Because logical block
+ * zram manages data in physical block size units. Because logical block
* size isn't identical with physical block size on some arch, we
- * could get discard request pointing to specific offset within certain
- * physical block. Although we can handle this request by reading that
- * physiclal block and decompressing and partially zeroing and
- * re-compressing and then re-storing it, it isn't reasonable because
- * our intention of handling discard request is to save memory.
- * So skipping this logical block is approriate here.
+ * could get a discard request pointing to a specific offset within a
+ * certain physical block. Although we can handle this request by
+ * reading that physiclal block and decompressing and partially zeroing
+ * and re-compressing and then re-storing it, this isn't reasonable
+ * because our intent with a discard request is to save memory. So
+ * skipping this logical block is appropriate here.
*/
if (offset) {
if (n < offset)
@@ -580,9 +580,8 @@ static void zram_bio_discard(struct zram
while (n >= PAGE_SIZE) {
/*
- * discard request can be too large so that the zram can
- * be stucked for a long time if we handle the request
- * at once. So handle the request by PAGE_SIZE unit at a time.
+ * Discard request can be large so the lock hold times could be
+ * lengthy. So take the lock once per page.
*/
write_lock(&zram->meta->tb_lock);
zram_free_page(zram, index);
@@ -907,9 +906,10 @@ static int create_device(struct zram *zr
/*
* zram_bio_discard() will clear all logical blocks if logical block
* size is identical with physical block size(PAGE_SIZE). But if it is
- * different, we will skip to discard some parts of logical blocks in
- * whole request range which isn't aligned to physical block size.
- * So we can't ensure that some discarded logical block is zeroed.
+ * different, we will skip discarding some parts of logical blocks in
+ * the part of the request range which isn't aligned to physical block
+ * size. So we can't ensure that all discarded logical blocks are
+ * zeroed.
*/
if (ZRAM_LOGICAL_BLOCK_SIZE == PAGE_SIZE)
zram->disk->queue->limits.discard_zeroes_data = 1;
_
--
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