I've been asked several very simple questions: a) How can I ensure that zram uses (or used) several compression streams? b) What is the current number of comp streams (how much memory does zram *actually* use for compression streams, if there are more than one stream)?
zram, indeed, does not provide any info and does not answer these questions. Reading from `max_comp_streams' let to estimate only theoretical comp streams memory consumption, which assumes that zram will allocate max_comp_streams. However, it's possible that the real number of compression streams will never reach that max value, due to various reasons, e.g. max_comp_streams is too high, etc. The patch adds `avail_streams' column to the /sys/block/zram<id>/mm_stat device file. For a single compression stream backend it's always 1, for a multi stream backend - it shows the actual ->avail_strm value. The number of allocated compression streams answers several questions: a) the current `level of concurrency' that the device has experienced b) the amount of memory used by compression streams (by multiplying the `avail_streams' column value, ->buffer size and algorithm's specific scratch buffer size; the last are easy to find out, unlike `avail_streams'). Signed-off-by: Sergey Senozhatsky <[email protected]> --- Documentation/blockdev/zram.txt | 9 +++++++++ drivers/block/zram/zcomp.c | 24 ++++++++++++++++++++++++ drivers/block/zram/zcomp.h | 2 ++ drivers/block/zram/zram_drv.c | 7 +++++-- 4 files changed, 40 insertions(+), 2 deletions(-) diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt index 5bda503..95bad79 100644 --- a/Documentation/blockdev/zram.txt +++ b/Documentation/blockdev/zram.txt @@ -227,6 +227,15 @@ line of text and contains the following stats separated by whitespace: mem_used_max zero_pages num_migrated + avail_streams + +`avail_streams' column shows the current number of available compression +streams, which is not necessarily equal to the number of max compression +streams. The number of max compression streams can be set too high and be +unreachable (depending on the load and the usage pattern, of course). +`avail_streams' let to find out the real 'level of concurrency' that +a particular zram device saw and to calculate the real memory consumption +by allocated compression streams, not the theoretical maximum value. 9) Deactivate: swapoff /dev/zram0 diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c index 3ef42e5..83ee2a4 100644 --- a/drivers/block/zram/zcomp.c +++ b/drivers/block/zram/zcomp.c @@ -183,6 +183,18 @@ static bool zcomp_strm_multi_set_max_streams(struct zcomp *comp, int num_strm) return true; } +static int zcomp_strm_multi_num_avail_streams(struct zcomp *comp) +{ + int avail; + struct zcomp_strm_multi *zs = comp->stream; + + spin_lock(&zs->strm_lock); + avail = zs->avail_strm; + spin_unlock(&zs->strm_lock); + + return avail; +} + static void zcomp_strm_multi_destroy(struct zcomp *comp) { struct zcomp_strm_multi *zs = comp->stream; @@ -206,6 +218,7 @@ static int zcomp_strm_multi_create(struct zcomp *comp, int max_strm) comp->strm_find = zcomp_strm_multi_find; comp->strm_release = zcomp_strm_multi_release; comp->set_max_streams = zcomp_strm_multi_set_max_streams; + comp->num_avail_streams = zcomp_strm_multi_num_avail_streams; zs = kmalloc(sizeof(struct zcomp_strm_multi), GFP_KERNEL); if (!zs) return -ENOMEM; @@ -246,6 +259,11 @@ static bool zcomp_strm_single_set_max_streams(struct zcomp *comp, int num_strm) return false; } +static int zcomp_strm_single_num_avail_streams(struct zcomp *comp) +{ + return 1; +} + static void zcomp_strm_single_destroy(struct zcomp *comp) { struct zcomp_strm_single *zs = comp->stream; @@ -261,6 +279,7 @@ static int zcomp_strm_single_create(struct zcomp *comp) comp->strm_find = zcomp_strm_single_find; comp->strm_release = zcomp_strm_single_release; comp->set_max_streams = zcomp_strm_single_set_max_streams; + comp->num_avail_streams = zcomp_strm_single_num_avail_streams; zs = kmalloc(sizeof(struct zcomp_strm_single), GFP_KERNEL); if (!zs) return -ENOMEM; @@ -304,6 +323,11 @@ bool zcomp_set_max_streams(struct zcomp *comp, int num_strm) return comp->set_max_streams(comp, num_strm); } +int zcomp_num_avail_streams(struct zcomp *comp) +{ + return comp->num_avail_streams(comp); +} + struct zcomp_strm *zcomp_strm_find(struct zcomp *comp) { return comp->strm_find(comp); diff --git a/drivers/block/zram/zcomp.h b/drivers/block/zram/zcomp.h index b7d2a4b..a69a3ca 100644 --- a/drivers/block/zram/zcomp.h +++ b/drivers/block/zram/zcomp.h @@ -47,6 +47,7 @@ struct zcomp { struct zcomp_strm *(*strm_find)(struct zcomp *comp); void (*strm_release)(struct zcomp *comp, struct zcomp_strm *zstrm); bool (*set_max_streams)(struct zcomp *comp, int num_strm); + int (*num_avail_streams)(struct zcomp *comp); void (*destroy)(struct zcomp *comp); }; @@ -66,4 +67,5 @@ int zcomp_decompress(struct zcomp *comp, const unsigned char *src, size_t src_len, unsigned char *dst); bool zcomp_set_max_streams(struct zcomp *comp, int num_strm); +int zcomp_num_avail_streams(struct zcomp *comp); #endif /* _ZCOMP_H_ */ diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 370c2f7..46055db 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -429,6 +429,7 @@ static ssize_t mm_stat_show(struct device *dev, struct zs_pool_stats pool_stats; u64 orig_size, mem_used = 0; long max_used; + int avail_streams = 0; ssize_t ret; memset(&pool_stats, 0x00, sizeof(struct zs_pool_stats)); @@ -437,20 +438,22 @@ static ssize_t mm_stat_show(struct device *dev, if (init_done(zram)) { mem_used = zs_get_total_pages(zram->meta->mem_pool); zs_pool_stats(zram->meta->mem_pool, &pool_stats); + avail_streams = zcomp_num_avail_streams(zram->comp); } orig_size = atomic64_read(&zram->stats.pages_stored); max_used = atomic_long_read(&zram->stats.max_used_pages); ret = scnprintf(buf, PAGE_SIZE, - "%8llu %8llu %8llu %8lu %8ld %8llu %8lu\n", + "%8llu %8llu %8llu %8lu %8ld %8llu %8lu %8d\n", orig_size << PAGE_SHIFT, (u64)atomic64_read(&zram->stats.compr_data_size), mem_used << PAGE_SHIFT, zram->limit_pages << PAGE_SHIFT, max_used << PAGE_SHIFT, (u64)atomic64_read(&zram->stats.zero_pages), - pool_stats.pages_compacted); + pool_stats.pages_compacted, + avail_streams); up_read(&zram->init_lock); return ret; -- 2.7.0.75.g3ee1e0f
