The patch titled
Subject: zram: writeback throttle
has been added to the -mm tree. Its filename is
zram-writeback-throttle-v4.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/zram-writeback-throttle-v4.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/zram-writeback-throttle-v4.patch
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 and is updated
there every 3-4 working days
------------------------------------------------------
From: Minchan Kim <minchan@xxxxxxxxxx>
Subject: zram: writeback throttle
If there are lots of write IO with flash device, it could have a
wearout problem of storage. To overcome the problem, admin needs
to design write limitation to guarantee flash health
for entire product life.
This patch creates a new knob "writeback_limit" on zram.
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.
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.
If admin want to allow further write again, he could do it like below
echo 0 > /sys/block/zram0/writeback_limit
If admin want to see remaining writeback budget,
cat /sys/block/zram0/writeback_limit
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.
Link: http://lkml.kernel.org/r/20181203024045.153534-8-minchan@xxxxxxxxxx
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/blockdev/zram.txt | 29 +++++++++++++++++++++++++++++
drivers/block/zram/zram_drv.c | 21 +++++++++++----------
2 files changed, 40 insertions(+), 10 deletions(-)
--- a/Documentation/blockdev/zram.txt~zram-writeback-throttle-v4
+++ a/Documentation/blockdev/zram.txt
@@ -277,6 +277,35 @@ Admin can request writeback of those idl
With the command, zram writeback idle pages from memory to the storage.
+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.
+
+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.
+
+If admin want to allow further write again, he could do it like below
+
+ echo 0 > /sys/block/zram0/writeback_limit
+
+If admin want to see remaining writeback budget since he set,
+
+ cat /sys/block/zram0/writeback_limit
+
+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.
+
= memory tracking
With CONFIG_ZRAM_MEMORY_TRACKING, user can know information of the
--- a/drivers/block/zram/zram_drv.c~zram-writeback-throttle-v4
+++ a/drivers/block/zram/zram_drv.c
@@ -330,7 +330,6 @@ next:
}
#ifdef CONFIG_ZRAM_WRITEBACK
-
static ssize_t writeback_limit_store(struct device *dev,
struct device_attribute *attr, const char *buf, size_t len)
{
@@ -343,7 +342,7 @@ static ssize_t writeback_limit_store(str
down_read(&zram->init_lock);
atomic64_set(&zram->stats.bd_wb_limit, val);
- if (val == 0 || val > atomic64_read(&zram->stats.bd_writes))
+ if (val == 0)
zram->stop_writeback = false;
up_read(&zram->init_lock);
ret = len;
@@ -605,7 +604,6 @@ static ssize_t writeback_store(struct de
char mode_buf[8];
unsigned long mode = -1UL;
unsigned long blk_idx = 0;
- u64 wb_count, wb_limit;
sz = strscpy(mode_buf, buf, sizeof(mode_buf));
if (sz <= 0)
@@ -710,7 +708,7 @@ static ssize_t writeback_store(struct de
continue;
}
- wb_count = atomic64_inc_return(&zram->stats.bd_writes);
+ atomic64_inc(&zram->stats.bd_writes);
/*
* We released zram_slot_lock so need to check if the slot was
* changed. If there is freeing for the slot, we can catch it
@@ -734,9 +732,11 @@ static ssize_t writeback_store(struct de
zram_set_element(zram, index, blk_idx);
blk_idx = 0;
atomic64_inc(&zram->stats.pages_stored);
- wb_limit = atomic64_read(&zram->stats.bd_wb_limit);
- if (wb_limit != 0 && wb_count >= wb_limit)
- zram->stop_writeback = true;
+ 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;
+ }
next:
zram_slot_unlock(zram, index);
}
@@ -1061,6 +1061,7 @@ static ssize_t mm_stat_show(struct devic
}
#ifdef CONFIG_ZRAM_WRITEBACK
+#define FOUR_K(x) ((x) * (1 << (PAGE_SHIFT - 12)))
static ssize_t bd_stat_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
@@ -1070,9 +1071,9 @@ static ssize_t bd_stat_show(struct devic
down_read(&zram->init_lock);
ret = scnprintf(buf, PAGE_SIZE,
"%8llu %8llu %8llu\n",
- (u64)atomic64_read(&zram->stats.bd_count) * (PAGE_SHIFT - 12),
- (u64)atomic64_read(&zram->stats.bd_reads) * (PAGE_SHIFT - 12),
- (u64)atomic64_read(&zram->stats.bd_writes) * (PAGE_SHIFT - 12));
+ FOUR_K((u64)atomic64_read(&zram->stats.bd_count)),
+ FOUR_K((u64)atomic64_read(&zram->stats.bd_reads)),
+ FOUR_K((u64)atomic64_read(&zram->stats.bd_writes)));
up_read(&zram->init_lock);
return ret;
_
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-add-bd_stat-statistics-v4.patch
zram-writeback-throttle.patch
zram-writeback-throttle-v4.patch
