The patch titled
Subject: Revert "zram: remove double compression logic"
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
revert-zram-remove-double-compression-logic.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/revert-zram-remove-double-compression-logic.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: Jiri Slaby <jslaby@xxxxxxx>
Subject: Revert "zram: remove double compression logic"
Date: Wed, 10 Aug 2022 09:06:09 +0200
This reverts commit e7be8d1dd983156b ("zram: remove double compression
logic") as it causes zram failures. It does not revert cleanly, PTR_ERR
handling was introduced in the meantime. This is handled by appropriate
IS_ERR.
When under memory pressure, zs_malloc() can fail. Before the above
commit, the allocation was retried with direct reclaim enabled (GFP_NOIO).
After the commit, it is not -- only __GFP_KSWAPD_RECLAIM is tried.
So when the failure occurs under memory pressure, the overlaying
filesystem such as ext2 (mounted by ext4 module in this case) can emit
failures, making the (file)system unusable:
EXT4-fs warning (device zram0): ext4_end_bio:343: I/O error 10 writing to inode 16386 starting block 159744)
Buffer I/O error on device zram0, logical block 159744
With direct reclaim, memory is really reclaimed and allocation succeeds,
eventually. In the worst case, the oom killer is invoked, which is proper
outcome if user sets up zram too large (in comparison to available RAM).
This very diff doesn't apply to 5.19 (stable) cleanly (see PTR_ERR note
above). Use revert of e7be8d1dd983 directly.
Link: https://bugzilla.suse.com/show_bug.cgi?id=1202203
Link: https://lkml.kernel.org/r/20220810070609.14402-1-jslaby@xxxxxxx
Fixes: e7be8d1dd983 ("zram: remove double compression logic")
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
Reviewed-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Nitin Gupta <ngupta@xxxxxxxxxx>
Cc: Alexey Romanov <avromanov@xxxxxxxxxxxxxx>
Cc: Dmitry Rokosov <ddrokosov@xxxxxxxxxxxxxx>
Cc: Lukas Czerner <lczerner@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [5.19]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/block/zram/zram_drv.c | 42 ++++++++++++++++++++++++--------
drivers/block/zram/zram_drv.h | 1
2 files changed, 33 insertions(+), 10 deletions(-)
--- a/drivers/block/zram/zram_drv.c~revert-zram-remove-double-compression-logic
+++ a/drivers/block/zram/zram_drv.c
@@ -1146,14 +1146,15 @@ static ssize_t bd_stat_show(struct devic
static ssize_t debug_stat_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
- int version = 2;
+ int version = 1;
struct zram *zram = dev_to_zram(dev);
ssize_t ret;
down_read(&zram->init_lock);
ret = scnprintf(buf, PAGE_SIZE,
- "version: %d\n%8llu\n",
+ "version: %d\n%8llu %8llu\n",
version,
+ (u64)atomic64_read(&zram->stats.writestall),
(u64)atomic64_read(&zram->stats.miss_free));
up_read(&zram->init_lock);
@@ -1351,7 +1352,7 @@ static int __zram_bvec_write(struct zram
{
int ret = 0;
unsigned long alloced_pages;
- unsigned long handle = 0;
+ unsigned long handle = -ENOMEM;
unsigned int comp_len = 0;
void *src, *dst, *mem;
struct zcomp_strm *zstrm;
@@ -1369,6 +1370,7 @@ static int __zram_bvec_write(struct zram
}
kunmap_atomic(mem);
+compress_again:
zstrm = zcomp_stream_get(zram->comp);
src = kmap_atomic(page);
ret = zcomp_compress(zstrm, src, &comp_len);
@@ -1377,20 +1379,39 @@ static int __zram_bvec_write(struct zram
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 = zs_malloc(zram->mem_pool, comp_len,
- __GFP_KSWAPD_RECLAIM |
- __GFP_NOWARN |
- __GFP_HIGHMEM |
- __GFP_MOVABLE);
-
+ /*
+ * 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 (IS_ERR((void *)handle))
+ handle = zs_malloc(zram->mem_pool, comp_len,
+ __GFP_KSWAPD_RECLAIM |
+ __GFP_NOWARN |
+ __GFP_HIGHMEM |
+ __GFP_MOVABLE);
if (IS_ERR((void *)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 (!IS_ERR((void *)handle))
+ goto compress_again;
return PTR_ERR((void *)handle);
}
@@ -1948,6 +1969,7 @@ 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;
--- a/drivers/block/zram/zram_drv.h~revert-zram-remove-double-compression-logic
+++ a/drivers/block/zram/zram_drv.h
@@ -81,6 +81,7 @@ 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 */
_
Patches currently in -mm which might be from jslaby@xxxxxxx are
revert-zram-remove-double-compression-logic.patch
