The patch titled
Subject: zram: idle writeback fixes and cleanup
has been added to the -mm tree. Its filename is
zram-idle-writeback-fixes-and-cleanup.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/zram-idle-writeback-fixes-and-cleanup.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/zram-idle-writeback-fixes-and-cleanup.patch
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------------------------------------------------------
From: Minchan Kim <minchan@xxxxxxxxxx>
Subject: zram: idle writeback fixes and cleanup
This patch includes some fixes and cleanup for idle-page writeback.
1. writeback_limit interface
Now writeback_limit interface is rather conusing. For example, once
writeback limit budget is exausted, admin can see 0 from
/sys/block/zramX/writeback_limit which is same semantic with disable
writeback_limit at this moment. IOW, admin cannot tell that zero came
from disable writeback limit or exausted writeback limit.
To make the interface clear, let's sepatate enable of writeback limit to
another knob - /sys/block/zram0/writeback_limit_enable
* before:
while true :
# to re-enable writeback limit once previous one is used up
echo 0 > /sys/block/zram0/writeback_limit
echo $((200<<20)) > /sys/block/zram0/writeback_limit
..
.. # used up the writeback limit budget
* new
# To enable writeback limit, from the beginning, admin should
# enable it.
echo $((200<<20)) > /sys/block/zram0/writeback_limit
echo 1 > /sys/block/zram/0/writeback_limit_enable
while true :
echo $((200<<20)) > /sys/block/zram0/writeback_limit
..
.. # used up the writeback limit budget
It's much strightforward.
2. fix condition check idle/huge writeback mode check
The mode in writeback_store is not bit opeartion any more so no need to
use bit operations. Furthermore, current condition check is broken in
that it does writeback every pages regardless of huge/idle.
3. clean up idle_store
No need to use goto.
Link: http://lkml.kernel.org/r/20181224033529.19450-1-minchan@xxxxxxxxxx
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
Suggested-by: John Dias <joaodias@xxxxxxxxxx>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@xxxxxxxxx>
Cc: John Dias <joaodias@xxxxxxxxxx>
Cc: Srinivas Paladugu <srnvs@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
--- a/Documentation/ABI/testing/sysfs-block-zram~zram-idle-writeback-fixes-and-cleanup
+++ a/Documentation/ABI/testing/sysfs-block-zram
@@ -122,11 +122,18 @@ Description:
statistics (bd_count, bd_reads, bd_writes) in a format
similar to block layer statistics file format.
+What: /sys/block/zram<id>/writeback_limit_enable
+Date: November 2018
+Contact: Minchan Kim <minchan@xxxxxxxxxx>
+Description:
+ The writeback_limit_enable file is read-write and specifies
+ eanbe of writeback_limit feature. "1" means eable the feature.
+ No limit "0" is the initial state.
+
What: /sys/block/zram<id>/writeback_limit
Date: November 2018
Contact: Minchan Kim <minchan@xxxxxxxxxx>
Description:
The writeback_limit file is read-write and specifies the maximum
amount of writeback ZRAM can do. The limit could be changed
- in run time and "0" means disable the limit.
- No limit is the initial state.
+ in run time.
--- a/Documentation/blockdev/zram.txt~zram-idle-writeback-fixes-and-cleanup
+++ a/Documentation/blockdev/zram.txt
@@ -156,22 +156,23 @@ Per-device statistics are exported as va
A brief description of exported device attributes. For more details please
read Documentation/ABI/testing/sysfs-block-zram.
-Name access description
----- ------ -----------
-disksize RW show and set the device's disk size
-initstate RO shows the initialization state of the device
-reset WO trigger device reset
-mem_used_max WO reset the `mem_used_max' counter (see later)
-mem_limit WO specifies the maximum amount of memory ZRAM can use
- to store the compressed data
-writeback_limit WO specifies the maximum amount of write IO zram can
- write out to backing device as 4KB unit
-max_comp_streams RW the number of possible concurrent compress operations
-comp_algorithm RW show and change the compression algorithm
-compact WO trigger memory compaction
-debug_stat RO this file is used for zram debugging purposes
-backing_dev RW set up backend storage for zram to write out
-idle WO mark allocated slot as idle
+Name access description
+---- ------ -----------
+disksize RW show and set the device's disk size
+initstate RO shows the initialization state of the device
+reset WO trigger device reset
+mem_used_max WO reset the `mem_used_max' counter (see later)
+mem_limit WO specifies the maximum amount of memory ZRAM can use
+ to store the compressed data
+writeback_limit WO specifies the maximum amount of write IO zram can
+ write out to backing device as 4KB unit
+writeback_limit_enable RW show and set writeback_limit feature
+max_comp_streams RW the number of possible concurrent compress operations
+comp_algorithm RW show and change the compression algorithm
+compact WO trigger memory compaction
+debug_stat RO this file is used for zram debugging purposes
+backing_dev RW set up backend storage for zram to write out
+idle WO mark allocated slot as idle
User space is advised to use the following files to read the device statistics.
@@ -280,32 +281,51 @@ With the command, zram writeback idle pa
If there are lots of write IO with flash device, potentially, it has
flash wearout problem so that admin needs to design write limitation
to guarantee storage health for entire product life.
-To overcome the concern, zram supports "writeback_limit".
-The "writeback_limit"'s default value is 0 so that it doesn't limit
-any writeback. If admin want to measure writeback count in a certain
-period, he could know it via /sys/block/zram0/bd_stat's 3rd column.
+
+To overcome the concern, zram supports "writeback_limit" feature.
+The "writeback_limit_enable"'s default value is 0 so that it doesn't limit
+any writeback. IOW, if admin want to apply writeback budget, he should
+enable writeback_limit_enable via
+
+ $ echo 1 > /sys/block/zramX/writeback_limit_enable
+
+Once writeback_limit_enable is set, zram doesn't allow any writeback
+until admin set the budget via /sys/block/zramX/writeback_limit.
+
+(If admin doesn't enable writeback_limit_enable, writeback_limit's value
+assigned via /sys/block/zramX/writeback_limit is meaninless.)
If admin want to limit writeback as per-day 400M, he could do it
like below.
- MB_SHIFT=20
- 4K_SHIFT=12
- echo $((400<<MB_SHIFT>>4K_SHIFT)) > \
- /sys/block/zram0/writeback_limit.
+ $ MB_SHIFT=20
+ $ 4K_SHIFT=12
+ $ echo $((400<<MB_SHIFT>>4K_SHIFT)) > \
+ /sys/block/zram0/writeback_limit.
+ $ echo 1 > /sys/block/zram0/writeback_limit_enable
-If admin want to allow further write again, he could do it like below
+If admin want to allow further write again once the bugdet is exausted,
+he could do it like below
- echo 0 > /sys/block/zram0/writeback_limit
+ $ echo $((400<<MB_SHIFT>>4K_SHIFT)) > \
+ /sys/block/zram0/writeback_limit
If admin want to see remaining writeback budget since he set,
- cat /sys/block/zram0/writeback_limit
+ $ cat /sys/block/zramX/writeback_limit
+
+If admin want to disable writeback limit, he could do
+
+ $ echo 0 > /sys/block/zramX/writeback_limit_enable
The writeback_limit count will reset whenever you reset zram(e.g.,
system reboot, echo 1 > /sys/block/zramX/reset) so keeping how many of
writeback happened until you reset the zram to allocate extra writeback
budget in next setting is user's job.
+If admin want to measure writeback count in a certain period, he could
+know it via /sys/block/zram0/bd_stat's 3rd column.
+
= memory tracking
With CONFIG_ZRAM_MEMORY_TRACKING, user can know information of the
--- a/drivers/block/zram/zram_drv.c~zram-idle-writeback-fixes-and-cleanup
+++ a/drivers/block/zram/zram_drv.c
@@ -316,11 +316,9 @@ static ssize_t idle_store(struct device
* See the comment in writeback_store.
*/
zram_slot_lock(zram, index);
- if (!zram_allocated(zram, index) ||
- zram_test_flag(zram, index, ZRAM_UNDER_WB))
- goto next;
- zram_set_flag(zram, index, ZRAM_IDLE);
-next:
+ if (zram_allocated(zram, index) &&
+ !zram_test_flag(zram, index, ZRAM_UNDER_WB))
+ zram_set_flag(zram, index, ZRAM_IDLE);
zram_slot_unlock(zram, index);
}
@@ -330,6 +328,41 @@ next:
}
#ifdef CONFIG_ZRAM_WRITEBACK
+static ssize_t writeback_limit_enable_store(struct device *dev,
+ struct device_attribute *attr, const char *buf, size_t len)
+{
+ struct zram *zram = dev_to_zram(dev);
+ u64 val;
+ ssize_t ret = -EINVAL;
+
+ if (kstrtoull(buf, 10, &val))
+ return ret;
+
+ down_read(&zram->init_lock);
+ spin_lock(&zram->wb_limit_lock);
+ zram->wb_limit_enable = val;
+ spin_unlock(&zram->wb_limit_lock);
+ up_read(&zram->init_lock);
+ ret = len;
+
+ return ret;
+}
+
+static ssize_t writeback_limit_enable_show(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ bool val;
+ struct zram *zram = dev_to_zram(dev);
+
+ down_read(&zram->init_lock);
+ spin_lock(&zram->wb_limit_lock);
+ val = zram->wb_limit_enable;
+ spin_unlock(&zram->wb_limit_lock);
+ up_read(&zram->init_lock);
+
+ return scnprintf(buf, PAGE_SIZE, "%d\n", val);
+}
+
static ssize_t writeback_limit_store(struct device *dev,
struct device_attribute *attr, const char *buf, size_t len)
{
@@ -341,9 +374,9 @@ static ssize_t writeback_limit_store(str
return ret;
down_read(&zram->init_lock);
- atomic64_set(&zram->stats.bd_wb_limit, val);
- if (val == 0)
- zram->stop_writeback = false;
+ spin_lock(&zram->wb_limit_lock);
+ zram->bd_wb_limit = val;
+ spin_unlock(&zram->wb_limit_lock);
up_read(&zram->init_lock);
ret = len;
@@ -357,7 +390,9 @@ static ssize_t writeback_limit_show(stru
struct zram *zram = dev_to_zram(dev);
down_read(&zram->init_lock);
- val = atomic64_read(&zram->stats.bd_wb_limit);
+ spin_lock(&zram->wb_limit_lock);
+ val = zram->bd_wb_limit;
+ spin_unlock(&zram->wb_limit_lock);
up_read(&zram->init_lock);
return scnprintf(buf, PAGE_SIZE, "%llu\n", val);
@@ -588,8 +623,8 @@ static int read_from_bdev_async(struct z
return 1;
}
-#define HUGE_WRITEBACK 0x1
-#define IDLE_WRITEBACK 0x2
+#define HUGE_WRITEBACK 1
+#define IDLE_WRITEBACK 2
static ssize_t writeback_store(struct device *dev,
struct device_attribute *attr, const char *buf, size_t len)
@@ -602,7 +637,7 @@ static ssize_t writeback_store(struct de
struct page *page;
ssize_t ret, sz;
char mode_buf[8];
- unsigned long mode = -1UL;
+ int mode = -1;
unsigned long blk_idx = 0;
sz = strscpy(mode_buf, buf, sizeof(mode_buf));
@@ -618,7 +653,7 @@ static ssize_t writeback_store(struct de
else if (!strcmp(mode_buf, "huge"))
mode = HUGE_WRITEBACK;
- if (mode == -1UL)
+ if (mode == -1)
return -EINVAL;
down_read(&zram->init_lock);
@@ -645,10 +680,13 @@ static ssize_t writeback_store(struct de
bvec.bv_len = PAGE_SIZE;
bvec.bv_offset = 0;
- if (zram->stop_writeback) {
+ spin_lock(&zram->wb_limit_lock);
+ if (zram->wb_limit_enable && !zram->bd_wb_limit) {
+ spin_unlock(&zram->wb_limit_lock);
ret = -EIO;
break;
}
+ spin_unlock(&zram->wb_limit_lock);
if (!blk_idx) {
blk_idx = alloc_block_bdev(zram);
@@ -667,10 +705,11 @@ static ssize_t writeback_store(struct de
zram_test_flag(zram, index, ZRAM_UNDER_WB))
goto next;
- if ((mode & IDLE_WRITEBACK &&
- !zram_test_flag(zram, index, ZRAM_IDLE)) &&
- (mode & HUGE_WRITEBACK &&
- !zram_test_flag(zram, index, ZRAM_HUGE)))
+ if (mode == IDLE_WRITEBACK &&
+ !zram_test_flag(zram, index, ZRAM_IDLE))
+ goto next;
+ if (mode == HUGE_WRITEBACK &&
+ !zram_test_flag(zram, index, ZRAM_HUGE))
goto next;
/*
* Clearing ZRAM_UNDER_WB is duty of caller.
@@ -732,11 +771,10 @@ static ssize_t writeback_store(struct de
zram_set_element(zram, index, blk_idx);
blk_idx = 0;
atomic64_inc(&zram->stats.pages_stored);
- if (atomic64_add_unless(&zram->stats.bd_wb_limit,
- -1 << (PAGE_SHIFT - 12), 0)) {
- if (atomic64_read(&zram->stats.bd_wb_limit) == 0)
- zram->stop_writeback = true;
- }
+ spin_lock(&zram->wb_limit_lock);
+ if (zram->wb_limit_enable && zram->bd_wb_limit > 0)
+ zram->bd_wb_limit -= 1UL << (PAGE_SHIFT - 12);
+ spin_unlock(&zram->wb_limit_lock);
next:
zram_slot_unlock(zram, index);
}
@@ -1812,6 +1850,7 @@ static DEVICE_ATTR_RW(comp_algorithm);
static DEVICE_ATTR_RW(backing_dev);
static DEVICE_ATTR_WO(writeback);
static DEVICE_ATTR_RW(writeback_limit);
+static DEVICE_ATTR_RW(writeback_limit_enable);
#endif
static struct attribute *zram_disk_attrs[] = {
@@ -1828,6 +1867,7 @@ static struct attribute *zram_disk_attrs
&dev_attr_backing_dev.attr,
&dev_attr_writeback.attr,
&dev_attr_writeback_limit.attr,
+ &dev_attr_writeback_limit_enable.attr,
#endif
&dev_attr_io_stat.attr,
&dev_attr_mm_stat.attr,
--- a/drivers/block/zram/zram_drv.h~zram-idle-writeback-fixes-and-cleanup
+++ a/drivers/block/zram/zram_drv.h
@@ -86,7 +86,6 @@ struct zram_stats {
atomic64_t bd_count; /* no. of pages in backing device */
atomic64_t bd_reads; /* no. of reads from backing device */
atomic64_t bd_writes; /* no. of writes from backing device */
- atomic64_t bd_wb_limit; /* writeback limit of backing device */
#endif
};
@@ -114,8 +113,10 @@ struct zram {
*/
bool claim; /* Protected by bdev->bd_mutex */
struct file *backing_dev;
- bool stop_writeback;
#ifdef CONFIG_ZRAM_WRITEBACK
+ spinlock_t wb_limit_lock;
+ bool wb_limit_enable;
+ u64 bd_wb_limit;
struct block_device *bdev;
unsigned int old_block_size;
unsigned long *bitmap;
_
Patches currently in -mm which might be from minchan@xxxxxxxxxx are
zram-fix-lockdep-warning-of-free-block-handling.patch
zram-fix-double-free-backing-device.patch
zram-refactoring-flags-and-writeback-stuff.patch
zram-introduce-zram_idle-flag.patch
zram-support-idle-huge-page-writeback.patch
zram-add-bd_stat-statistics.patch
zram-writeback-throttle.patch
zram-idle-writeback-fixes-and-cleanup.patch
