Re: [PATCH] zram: auto add/del devices on demand

From: Timofey Titovets
Date: Thu Jul 17 2014 - 07:21:37 EST


Thanks for comments, i will fix what you say and split patches one for code and one for Documentation.
After, i will resend patch set

On 07/17/2014 01:09 PM, Jerome Marchand wrote:
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On 07/17/2014 11:32 AM, Timofey Titovets wrote:
From: Timofey Titovets <nefelim4ag@xxxxxxxxx>

This add supporting of autochange count of zram devices on demand,
like loop devices; This working by following rules: - Always save
minimum devices count specified by num_device (can be specified
while kernel module loading) - if last device already using add new
device; - if last and prelast devices is free - delete last zram
device;


Hi Timofey,

Your patch change zram behaviour. Please describe what changes from
the user point of view and update Documentation/blockdev/zram.txt
accordingly.

Signed-off-by: Timofey Titovets <nefelim4ag@xxxxxxxxx>

Please pull from: https://github.com/Nefelim4ag/linux.git ---
Tested on 3.15.5-2-ARCH, can be applied on any kernel version after
this patch 'zram: add LZ4 compression support' -
https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/commit/?id=6e76668e415adf799839f0ab205142ad7002d260

--- drivers/block/zram/zram_drv.c | 65
++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 61
insertions(+), 4 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c
b/drivers/block/zram/zram_drv.c index 089e72c..d0a3055 100644 ---
a/drivers/block/zram/zram_drv.c +++
b/drivers/block/zram/zram_drv.c @@ -42,6 +42,10 @@ static const
char *default_compressor = "lzo";

/* Module params (documentation at end) */ static unsigned int
num_devices = 1; +static unsigned int last_created_dev = 1; +
+static void zram_add_dev(void); +static void zram_del_dev(void);

#define ZRAM_ATTR_RO(name) \ static ssize_t
zram_attr_##name##_show(struct device *d, \ @@ -168,6 +172,7
@@ static ssize_t comp_algorithm_store(struct device *dev, struct
device_attribute *attr, const char *buf, size_t len) { struct zram
*zram = dev_to_zram(dev); + down_write(&zram->init_lock); if
(init_done(zram)) { up_write(&zram->init_lock); @@ -239,6 +244,7 @@
static struct zram_meta *zram_meta_alloc(u64 disksize) { size_t
num_pages; struct zram_meta *meta = kmalloc(sizeof(*meta),
GFP_KERNEL); + if (!meta) goto out;

@@ -374,6 +380,7 @@ static int zram_bvec_read(struct zram *zram,
struct bio_vec *bvec, struct page *page; unsigned char *user_mem,
*uncmem = NULL; struct zram_meta *meta = zram->meta; + page =
bvec->bv_page;

read_lock(&meta->tb_lock); @@ -607,6 +614,7 @@ static void
zram_reset_device(struct zram *zram, bool reset_capacity) /* Free
all pages that are still in this zram device */ for (index = 0;
index < zram->disksize >> PAGE_SHIFT; index++) { unsigned long
handle = meta->table[index].handle; + if (!handle) continue;

@@ -668,6 +676,7 @@ static ssize_t disksize_store(struct device
*dev, set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT);
revalidate_disk(zram->disk); up_write(&zram->init_lock); +
zram_add_dev(); return len;

out_destroy_comp: @@ -712,6 +721,7 @@ static ssize_t
reset_store(struct device *dev, bdput(bdev);

zram_reset_device(zram, true); + zram_del_dev(); return len;

out: @@ -954,6 +964,51 @@ static void destroy_device(struct zram
*zram) blk_cleanup_queue(zram->queue); }

+/* remove last free device, if last and prelast dev a free */
+static void zram_del_dev(void) +{ + if (last_created_dev <
num_devices) + return; + + if
(zram_devices[last_created_dev].disksize == 0 && +
zram_devices[last_created_dev-1].disksize == 0 + ) { +
destroy_device(&zram_devices[last_created_dev]); +
last_created_dev--; + pr_info("Deleted zram%u device\n",
last_created_dev); + } +} + +/* Auto add empty zram device, if
last device in use */ +static void zram_add_dev(void) +{ + int
ret; + + if (last_created_dev+1 > max_num_devices) { +
pr_warn("Can't add zram%u, max device number reached\n", +
num_devices); + last_created_dev--; + ret = -EINVAL;

Why do you set ret to EINVAL here? It's never used.

+ goto out;

That label is useless. Just use return.

+ } + + if (&zram_devices[last_created_dev].disksize > 0) { +
last_created_dev++; + ret =
create_device(&zram_devices[last_created_dev], +
last_created_dev); + if (ret) + goto free;

If ret is only used to test that create_device() succeeded, then we
can get rid of that variable altogether.

Thanks,
Jerome

+ pr_info("Created zram%u device\n", last_created_dev); +
} + + return; + +free: +
destroy_device(&zram_devices[last_created_dev]); +
last_created_dev--; +out:; +} + static int __init zram_init(void)
{ int ret, dev_id; @@ -972,18 +1027,20 @@ static int __init
zram_init(void) goto out; }

- /* Allocate the device array and initialize each one */ -
zram_devices = kzalloc(num_devices * sizeof(struct zram),
GFP_KERNEL); + /* Allocate the device array */ + zram_devices
= kcalloc(max_num_devices, sizeof(struct zram), GFP_KERNEL); if
(!zram_devices) { ret = -ENOMEM; goto unregister; }

+ /* Initialise zram{0..num_devices} */ for (dev_id = 0; dev_id
< num_devices; dev_id++) { ret =
create_device(&zram_devices[dev_id], dev_id); if (ret) goto
free_devices; } + last_created_dev = num_devices-1;

pr_info("Created %u device(s) ...\n", num_devices);

@@ -1004,7 +1061,7 @@ static void __exit zram_exit(void) int i;
struct zram *zram;

- for (i = 0; i < num_devices; i++) { + for (i = 0; i <
last_created_dev+1; i++) { zram = &zram_devices[i];

destroy_device(zram); @@ -1025,7 +1082,7 @@
module_init(zram_init); module_exit(zram_exit);

module_param(num_devices, uint, 0); -MODULE_PARM_DESC(num_devices,
"Number of zram devices"); +MODULE_PARM_DESC(num_devices, "Number
of pre created zram devices");

MODULE_LICENSE("Dual BSD/GPL"); MODULE_AUTHOR("Nitin Gupta
<ngupta@xxxxxxxxxx>");

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