Hello Minchan,
the idea looks good and this is something I was trying to do, except
that I used kref.
some review nitpicks are below. I also posted modified version of your
patch so that will save some time.
> static inline int init_done(struct zram *zram)
> {
> - return zram->meta != NULL;
> + return zram->disksize != 0;
we don't set ->disksize to 0 when create device. and I think
it's better to use refcount here, but set it to 0 during device creation.
(see the patch below)
> +static inline bool zram_meta_get(struct zram_meta *meta)
> +{
> + if (!atomic_inc_not_zero(&meta->refcount))
> + return false;
> + return true;
> +}
I've changed it to likely case first: `if recount return true'
> static void zram_reset_device(struct zram *zram, bool reset_capacity)
> {
> + struct zram_meta *meta;
> + u64 disksize;
not needed. (see the patch below).
> +
> down_write(&zram->init_lock);
>
> zram->limit_pages = 0;
> @@ -728,14 +750,20 @@ static void zram_reset_device(struct zram *zram, bool
> reset_capacity)
> return;
> }
>
> + meta = zram->meta;
> +
> zcomp_destroy(zram->comp);
we can't destoy zcomp before we see IO completion.
> zram->max_comp_streams = 1;
we better keep original comp_streams number before we see IO completion.
we don't know how many RW ops we have, so completion can happen earlier.
> - zram_meta_free(zram->meta, zram->disksize);
> - zram->meta = NULL;
> + disksize = zram->disksize;
> + zram_meta_put(meta);
> + /* Read/write handler will not handle further I/O operation. */
> + zram->disksize = 0;
I keep it on its current position. (see below)
> + wait_for_completion(&meta->complete);
> + /* I/O operation under all of CPU are done so let's free */
> + zram_meta_free(zram->meta, disksize);
> /* Reset stats */
> memset(&zram->stats, 0, sizeof(zram->stats));
>
> - zram->disksize = 0;
> if (reset_capacity)
> set_capacity(zram->disk, 0);
>
> @@ -908,23 +936,25 @@ static void zram_make_request(struct request_queue
> *queue, struct bio *bio)
> {
> struct zram *zram = queue->queuedata;
>
> - down_read(&zram->init_lock);
> - if (unlikely(!init_done(zram)))
> + if (unlikely(!zram_meta_get(zram->meta)))
> goto error;
>
> + if (unlikely(!init_done(zram)))
> + goto put_meta;
> +
here and later:
we can't take zram_meta_get() first and then check for init_done(zram),
because ->meta can be NULL, so it fill be ->NULL->refcount.
let's keep ->completion and ->refcount in zram and rename zram_meta_[get|put]
to zram_[get|put].
please review a bit modified version of your patch.
/* the patch also reogranizes a bit order of struct zram members, to move
member that we use more often together and to avoid paddings. nothing
critical here. */
next action items are:
-- we actually can now switch from init_lock in some _show() fucntion to
zram_get()/zram_put()
-- address that theoretical and very unlikely in real live race condition
of umount-reset vs. mount-rw.
no concerns about performance of this version -- we probably will not get
any faster than that.
thanks a lot for your effort!
---
drivers/block/zram/zram_drv.c | 82 ++++++++++++++++++++++++++++++-------------
drivers/block/zram/zram_drv.h | 17 ++++-----
2 files changed, 66 insertions(+), 33 deletions(-)
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index aa5a4c5..6916790 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -44,7 +44,7 @@ static const char *default_compressor = "lzo";
static unsigned int num_devices = 1;
#define ZRAM_ATTR_RO(name) \
-static ssize_t name##_show(struct device *d, \
+static ssize_t name##_show(struct device *d, \
struct device_attribute *attr, char *b) \
{ \
struct zram *zram = dev_to_zram(d); \
@@ -55,7 +55,7 @@ static DEVICE_ATTR_RO(name);
static inline int init_done(struct zram *zram)
{
- return zram->meta != NULL;
+ return atomic_read(&zram->refcount);
}
static inline struct zram *dev_to_zram(struct device *dev)
@@ -358,6 +358,23 @@ out_error:
return NULL;
}
+static inline bool zram_get(struct zram *zram)
+{
+ if (atomic_inc_not_zero(&zram->refcount))
+ return true;
+ return false;
+}
+
+/*
+ * We want to free zram_meta in process context to avoid
+ * deadlock between reclaim path and any other locks
+ */
+static inline void zram_put(struct zram *zram)
+{
+ if (atomic_dec_and_test(&zram->refcount))
+ complete(&zram->io_done);
+}
+
static void update_position(u32 *index, int *offset, struct bio_vec *bvec)
{
if (*offset + bvec->bv_len >= PAGE_SIZE)
@@ -719,6 +736,9 @@ static void zram_bio_discard(struct zram *zram, u32 index,
static void zram_reset_device(struct zram *zram, bool reset_capacity)
{
+ struct zram_meta *meta;
+ struct zcomp *comp;
+
down_write(&zram->init_lock);
zram->limit_pages = 0;
@@ -728,14 +748,21 @@ static void zram_reset_device(struct zram *zram, bool
reset_capacity)
return;
}
- zcomp_destroy(zram->comp);
- zram->max_comp_streams = 1;
- zram_meta_free(zram->meta, zram->disksize);
- zram->meta = NULL;
+ meta = zram->meta;
+ comp = zram->comp;
+ /* ->refcount will go down to 0 eventually */
+ zram_put(zram);
+
+ wait_for_completion(&zram->io_done);
+ /* I/O operation under all of CPU are done so let's free */
+ zram_meta_free(meta, disksize);
+ zcomp_destroy(comp);
+
/* Reset stats */
memset(&zram->stats, 0, sizeof(zram->stats));
-
zram->disksize = 0;
+ zram->max_comp_streams = 1;
+
if (reset_capacity)
set_capacity(zram->disk, 0);
@@ -783,6 +810,8 @@ static ssize_t disksize_store(struct device *dev,
goto out_destroy_comp;
}
+ init_completion(&zram->io_done);
+ atomic_set(&zram->refcount, 1);
zram->meta = meta;
zram->comp = comp;
zram->disksize = disksize;
@@ -795,7 +824,6 @@ static ssize_t disksize_store(struct device *dev,
* so that revalidate_disk always sees up-to-date capacity.
*/
revalidate_disk(zram->disk);
-
return len;
out_destroy_comp:
@@ -908,23 +936,24 @@ static void zram_make_request(struct request_queue
*queue, struct bio *bio)
{
struct zram *zram = queue->queuedata;
- down_read(&zram->init_lock);
- if (unlikely(!init_done(zram)))
+ if (unlikely(!zram_get(zram)))
goto error;
+ if (unlikely(!init_done(zram)))
+ goto put_zram;
+
if (!valid_io_request(zram, bio->bi_iter.bi_sector,
bio->bi_iter.bi_size)) {
atomic64_inc(&zram->stats.invalid_io);
- goto error;
+ goto put_zram;
}
__zram_make_request(zram, bio);
- up_read(&zram->init_lock);
-
+ zram_put(zram);
return;
-
+put_zram:
+ zram_put(zram);
error:
- up_read(&zram->init_lock);
bio_io_error(bio);
}
@@ -946,21 +975,22 @@ static void zram_slot_free_notify(struct block_device
*bdev,
static int zram_rw_page(struct block_device *bdev, sector_t sector,
struct page *page, int rw)
{
- int offset, err;
+ int offset, err = -EIO;
u32 index;
struct zram *zram;
struct bio_vec bv;
zram = bdev->bd_disk->private_data;
+ if (unlikely(!zram_get(zram)))
+ goto out;
+
+ if (unlikely(!init_done(zram)))
+ goto put_zram;
+
if (!valid_io_request(zram, sector, PAGE_SIZE)) {
atomic64_inc(&zram->stats.invalid_io);
- return -EINVAL;
- }
-
- down_read(&zram->init_lock);
- if (unlikely(!init_done(zram))) {
- err = -EIO;
- goto out_unlock;
+ err = -EINVAL;
+ goto put_zram;
}
index = sector >> SECTORS_PER_PAGE_SHIFT;
@@ -971,8 +1001,9 @@ static int zram_rw_page(struct block_device *bdev,
sector_t sector,
bv.bv_offset = 0;
err = zram_bvec_rw(zram, &bv, index, offset, rw);
-out_unlock:
- up_read(&zram->init_lock);
+put_zram:
+ zram_put(zram);
+out:
/*
* If I/O fails, just return error(ie, non-zero) without
* calling page_endio.
@@ -1041,6 +1072,7 @@ static int create_device(struct zram *zram, int device_id)
int ret = -ENOMEM;
init_rwsem(&zram->init_lock);
+ atomic_set(&zram->refcount, 0);
zram->queue = blk_alloc_queue(GFP_KERNEL);
if (!zram->queue) {
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index b05a816..7138c82 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -100,24 +100,25 @@ struct zram_meta {
struct zram {
struct zram_meta *meta;
+ struct zcomp *comp;
struct request_queue *queue;
struct gendisk *disk;
- struct zcomp *comp;
-
/* Prevent concurrent execution of device init, reset and R/W request */
struct rw_semaphore init_lock;
/*
- * This is the limit on amount of *uncompressed* worth of data
- * we can store in a disk.
+ * the number of pages zram can consume for storing compressed data
*/
- u64 disksize; /* bytes */
+ unsigned long limit_pages;
+ atomic_t refcount;
int max_comp_streams;
+
struct zram_stats stats;
+ struct completion io_done; /* notify IO under all of cpu are done */
/*
- * the number of pages zram can consume for storing compressed data
+ * This is the limit on amount of *uncompressed* worth of data
+ * we can store in a disk.
*/
- unsigned long limit_pages;
-
+ u64 disksize; /* bytes */
char compressor[10];
};
#endif
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