On 11/27/2012 06:13 AM, Nitin Gupta wrote: > On 11/22/2012 06:42 PM, Minchan Kim wrote: >> Lockdep complains about recursive deadlock of zram->init_lock. >> Because zram_init_device could be called in reclaim context and >> it requires a page with GFP_KERNEL. >> >> We can fix it via replacing GFP_KERNEL with GFP_NOIO. >> But more big problem is vzalloc in zram_init_device which calls GFP_KERNEL. >> We can change it with __vmalloc which can receive gfp_t. >> But still we have a problem. Although __vmalloc can handle gfp_t, it calls >> allocation of GFP_KERNEL. That's why I sent the patch. >> https://lkml.org/lkml/2012/4/23/77 >> >> Yes. Fundamental problem is utter crap API vmalloc. >> If we can fix it, everyone would be happy. But life isn't simple >> like seeing my thread of the patch. >> >> So next option is to give up lazy initialization and initialize it at the >> very disksize setting time. But it makes unnecessary metadata waste until >> zram is really used. But let's think about it. >> >> 1) User of zram normally do mkfs.xxx or mkswap before using >> the zram block device(ex, normally, do it at booting time) >> It ends up allocating such metadata of zram before real usage so >> benefit of lazy initialzation would be mitigated. >> >> 2) Some user want to use zram when memory pressure is high.(ie, load zram >> dynamically, NOT booting time). It does make sense because people don't >> want to waste memory until memory pressure is high(ie, where zram is really >> helpful time). In this case, lazy initialzation could be failed easily >> because we will use GFP_NOIO instead of GFP_KERNEL for avoiding deadlock. >> So the benefit of lazy initialzation would be mitigated, too. >> >> 3) Metadata overhead is not critical and Nitin has a plan to diet it. >> 4K : 12 byte(64bit machine) -> 64G : 192M so 0.3% isn't big overhead >> If insane user use such big zram device up to 20, it could consume 6% of ram >> but efficieny of zram will cover the waste. >> >> So this patch gives up lazy initialization and instead we initialize metadata >> at disksize setting time. >> >> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> >> --- >> drivers/staging/zram/zram_drv.c | 21 ++++----------------- >> drivers/staging/zram/zram_sysfs.c | 1 + >> 2 files changed, 5 insertions(+), 17 deletions(-) >> >> diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c >> index 9ef1eca..f364fb5 100644 >> --- a/drivers/staging/zram/zram_drv.c >> +++ b/drivers/staging/zram/zram_drv.c >> @@ -441,16 +441,13 @@ static void zram_make_request(struct request_queue *queue, struct bio *bio) >> { >> struct zram *zram = queue->queuedata; >> >> - if (unlikely(!zram->init_done) && zram_init_device(zram)) >> - goto error; >> - >> down_read(&zram->init_lock); >> if (unlikely(!zram->init_done)) >> - goto error_unlock; >> + goto error; >> >> if (!valid_io_request(zram, bio)) { >> zram_stat64_inc(zram, &zram->stats.invalid_io); >> - goto error_unlock; >> + goto error; >> } >> >> __zram_make_request(zram, bio, bio_data_dir(bio)); >> @@ -458,9 +455,8 @@ static void zram_make_request(struct request_queue *queue, struct bio *bio) >> >> return; >> >> -error_unlock: >> - up_read(&zram->init_lock); >> error: >> + up_read(&zram->init_lock); >> bio_io_error(bio); >> } >> >> @@ -509,19 +505,12 @@ void zram_reset_device(struct zram *zram) >> up_write(&zram->init_lock); >> } >> >> +/* zram->init_lock should be hold */ > > s/hold/held > > btw, shouldn't we also change GFP_KERNEL to GFP_NOIO in is_partial_io() > case in both read/write handlers? Good point. Actually, the one in zram_bvec_read() should actually be GFP_ATOMIC because of the kmap_atomic() above (or be moved out of kmap_atomic/kunmap_atomic nest). Another solution would be to allocate some working buffer at device init as it's done for compress_buffer/workmem. It would make zram_bvec_read/write look simpler (no need to free memory or manage kmalloc failure). Jerome > > Rest of the patch looks good. > > > Thanks, > Nitin > >> int zram_init_device(struct zram *zram) >> { >> int ret; >> size_t num_pages; >> >> - down_write(&zram->init_lock); >> - if (zram->init_done) { >> - up_write(&zram->init_lock); >> - return 0; >> - } >> - >> - BUG_ON(!zram->disksize); >> - >> if (zram->disksize > 2 * (totalram_pages << PAGE_SHIFT)) { >> pr_info( >> "There is little point creating a zram of greater than " >> @@ -570,7 +559,6 @@ int zram_init_device(struct zram *zram) >> } >> >> zram->init_done = 1; >> - up_write(&zram->init_lock); >> >> pr_debug("Initialization done!\n"); >> return 0; >> @@ -580,7 +568,6 @@ fail_no_table: >> zram->disksize = 0; >> fail: >> __zram_reset_device(zram); >> - up_write(&zram->init_lock); >> pr_err("Initialization failed: err=%d\n", ret); >> return ret; >> } >> diff --git a/drivers/staging/zram/zram_sysfs.c b/drivers/staging/zram/zram_sysfs.c >> index 4143af9..369db12 100644 >> --- a/drivers/staging/zram/zram_sysfs.c >> +++ b/drivers/staging/zram/zram_sysfs.c >> @@ -71,6 +71,7 @@ static ssize_t disksize_store(struct device *dev, >> >> zram->disksize = PAGE_ALIGN(disksize); >> set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT); >> + zram_init_device(zram); >> up_write(&zram->init_lock); >> >> return len; >> > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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