The 2nd trial allocation under per-cpu presumption has been used to
prevent regression of allocation failure. However, it makes trouble
for maintenance without significant benefit. The slowpath branch is
executed extremely rarely: getting there is problematic. Therefore,
we delete this branch.
Since b09ab054b69b, zram has used QUEUE_FLAG_STABLE_WRITES to prevent
buffer change between 1st and 2nd memory allocations. Since we remove
second trial memory allocation logic, we could remove the STABLE_WRITES
flag because there is no change buffer to be modified under us.
Signed-off-by: Alexey Romanov <[email protected]>
Signed-off-by: Dmitry Rokosov <[email protected]>
---
drivers/block/zram/zram_drv.c | 42 +++++++++--------------------------
drivers/block/zram/zram_drv.h | 1 -
2 files changed, 10 insertions(+), 33 deletions(-)
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index cb253d80d72b..e10066a10dcf 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1147,15 +1147,14 @@ static ssize_t bd_stat_show(struct device *dev,
static ssize_t debug_stat_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
- int version = 1;
+ int version = 2;
struct zram *zram = dev_to_zram(dev);
ssize_t ret;
down_read(&zram->init_lock);
ret = scnprintf(buf, PAGE_SIZE,
- "version: %d\n%8llu %8llu\n",
+ "version: %d\n%8llu\n",
version,
- (u64)atomic64_read(&zram->stats.writestall),
(u64)atomic64_read(&zram->stats.miss_free));
up_read(&zram->init_lock);
@@ -1373,7 +1372,6 @@ static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
}
kunmap_atomic(mem);
-compress_again:
zstrm = zcomp_stream_get(zram->comp);
src = kmap_atomic(page);
ret = zcomp_compress(zstrm, src, &comp_len);
@@ -1382,39 +1380,20 @@ static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
if (unlikely(ret)) {
zcomp_stream_put(zram->comp);
pr_err("Compression failed! err=%d\n", ret);
- zs_free(zram->mem_pool, handle);
return ret;
}
if (comp_len >= huge_class_size)
comp_len = PAGE_SIZE;
- /*
- * handle allocation has 2 paths:
- * a) fast path is executed with preemption disabled (for
- * per-cpu streams) and has __GFP_DIRECT_RECLAIM bit clear,
- * since we can't sleep;
- * b) slow path enables preemption and attempts to allocate
- * the page with __GFP_DIRECT_RECLAIM bit set. we have to
- * put per-cpu compression stream and, thus, to re-do
- * the compression once handle is allocated.
- *
- * if we have a 'non-null' handle here then we are coming
- * from the slow path and handle has already been allocated.
- */
- if (!handle)
- handle = zs_malloc(zram->mem_pool, comp_len,
- __GFP_KSWAPD_RECLAIM |
- __GFP_NOWARN |
- __GFP_HIGHMEM |
- __GFP_MOVABLE);
- if (!handle) {
+
+ handle = zs_malloc(zram->mem_pool, comp_len,
+ __GFP_KSWAPD_RECLAIM |
+ __GFP_NOWARN |
+ __GFP_HIGHMEM |
+ __GFP_MOVABLE);
+
+ if (unlikely(!handle)) {
zcomp_stream_put(zram->comp);
- atomic64_inc(&zram->stats.writestall);
- handle = zs_malloc(zram->mem_pool, comp_len,
- GFP_NOIO | __GFP_HIGHMEM |
- __GFP_MOVABLE);
- if (handle)
- goto compress_again;
return -ENOMEM;
}
@@ -1975,7 +1954,6 @@ static int zram_add(void)
if (ZRAM_LOGICAL_BLOCK_SIZE == PAGE_SIZE)
blk_queue_max_write_zeroes_sectors(zram->disk->queue, UINT_MAX);
- blk_queue_flag_set(QUEUE_FLAG_STABLE_WRITES, zram->disk->queue);
ret = device_add_disk(NULL, zram->disk, zram_disk_groups);
if (ret)
goto out_cleanup_disk;
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index 80c3b43b4828..158c91e54850 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -81,7 +81,6 @@ struct zram_stats {
atomic64_t huge_pages_since; /* no. of huge pages since zram set up */
atomic64_t pages_stored; /* no. of pages currently stored */
atomic_long_t max_used_pages; /* no. of maximum pages stored */
- atomic64_t writestall; /* no. of write slow paths */
atomic64_t miss_free; /* no. of missed free */
#ifdef CONFIG_ZRAM_WRITEBACK
atomic64_t bd_count; /* no. of pages in backing device */
--
2.30.1
On Thu, May 05, 2022 at 12:44:43PM +0300, Alexey Romanov wrote:
> The 2nd trial allocation under per-cpu presumption has been used to
> prevent regression of allocation failure. However, it makes trouble
> for maintenance without significant benefit. The slowpath branch is
> executed extremely rarely: getting there is problematic. Therefore,
> we delete this branch.
>
> Since b09ab054b69b, zram has used QUEUE_FLAG_STABLE_WRITES to prevent
> buffer change between 1st and 2nd memory allocations. Since we remove
> second trial memory allocation logic, we could remove the STABLE_WRITES
> flag because there is no change buffer to be modified under us.
>
> Signed-off-by: Alexey Romanov <[email protected]>
> Signed-off-by: Dmitry Rokosov <[email protected]>
Acked-by: Minchan Kim <[email protected]>
On (22/05/05 12:44), Alexey Romanov wrote:
> @@ -1975,7 +1954,6 @@ static int zram_add(void)
> if (ZRAM_LOGICAL_BLOCK_SIZE == PAGE_SIZE)
> blk_queue_max_write_zeroes_sectors(zram->disk->queue, UINT_MAX);
>
> - blk_queue_flag_set(QUEUE_FLAG_STABLE_WRITES, zram->disk->queue);
By the way, why did it remove QUEUE_FLAG_STABLE_WRITES bit?
Hi Sergey,
On Tue, Aug 09, 2022 at 09:41:22PM +0900, Sergey Senozhatsky wrote:
> On (22/05/05 12:44), Alexey Romanov wrote:
> > @@ -1975,7 +1954,6 @@ static int zram_add(void)
> > if (ZRAM_LOGICAL_BLOCK_SIZE == PAGE_SIZE)
> > blk_queue_max_write_zeroes_sectors(zram->disk->queue, UINT_MAX);
> >
> > - blk_queue_flag_set(QUEUE_FLAG_STABLE_WRITES, zram->disk->queue);
>
> By the way, why did it remove QUEUE_FLAG_STABLE_WRITES bit?
Minchan asked me to add this change and this description:
"Since b09ab054b69b, zram has used QUEUE_FLAG_STABLE_WRITES to prevent
buffer change between 1st and 2nd memory allocations. Since we remove
second trial memory allocation logic, we could remove the STABLE_WRITES
flag because there is no change buffer to be modified under us"
This seems to be logical.
--
Thank you,
Alexey