Messages in this thread |  | | Date | Tue, 25 Feb 2014 01:11:30 +0900 | Subject | Re: [PATCH] zram: support REQ_DISCARD | From | Joonsoo Kim <> |
| |
2014-02-25 1:06 GMT+09:00 Jerome Marchand <jmarchan@redhat.com>: > On 02/24/2014 04:56 PM, Joonsoo Kim wrote: >> 2014-02-25 0:15 GMT+09:00 Jerome Marchand <jmarchan@redhat.com>: >>> On 02/24/2014 04:02 PM, Joonsoo Kim wrote: >>>> 2014-02-24 22:36 GMT+09:00 Jerome Marchand <jmarchan@redhat.com>: >>>>> On 02/24/2014 06:51 AM, Joonsoo Kim wrote: >>>>>> zram is ram based block device and can be used by backend of filesystem. >>>>>> When filesystem deletes a file, it normally doesn't do anything on data >>>>>> block of that file. It just marks on metadata of that file. This behavior >>>>>> has no problem on disk based block device, but has problems on ram based >>>>>> block device, since we can't free memory used for data block. To overcome >>>>>> this disadvantage, there is REQ_DISCARD functionality. If block device >>>>>> support REQ_DISCARD and filesystem is mounted with discard option, >>>>>> filesystem sends REQ_DISCARD to block device whenever some data blocks are >>>>>> discarded. All we have to do is to handle this request. >>>>>> >>>>>> This patch implements to flag up QUEUE_FLAG_DISCARD and handle this >>>>>> REQ_DISCARD request. With it, we can free memory used by zram if it isn't >>>>>> used. >>>>>> >>>>>> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com> >>>>>> --- >>>>>> This patch is based on master branch of linux-next tree. >>>>>> >>>>>> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c >>>>>> index 5ec61be..cff2c0e 100644 >>>>>> --- a/drivers/block/zram/zram_drv.c >>>>>> +++ b/drivers/block/zram/zram_drv.c >>>>>> @@ -501,6 +501,20 @@ static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index, >>>>>> return ret; >>>>>> } >>>>>> >>>>>> +static void zram_bio_discard(struct zram *zram, struct bio *bio) >>>>>> +{ >>>>>> + u32 index = bio->bi_iter.bi_sector >> SECTORS_PER_PAGE_SHIFT; >>>>> >>>>> Hi Joonsoo, >>>>> >>>>> If bi_sector is not aligned on a page size, we might end up discarding >>>>> a page that still contain valid data. >>>>> >>>>> >>>> >>>> Hello, Jerome. >>>> >>>> Is it possible that request isn't aligned on a page size if >>>> logical/physical block size >>>> is PAGE_SIZE? >>> >>> Yes, zram has an logical block size of 4k (ZRAM_LOGICAL_BLOCK_SIZE), >>> while its physical block size, which is a page size, can be bigger. >>> >>>> When I tested it, I didn't find any invalid io. >>>> If we meet any misaligned request, it would be filtered by >>>> valid_io_request(). :) >>> >>> zram accepts request aligned on logical blocks. So valid_io_request() >>> wouldn't filter misaligned requests out as long as they are aligned >>> on logical blocks. >>> If your system use 4k pages, your tests would never trigger the issue, >>> but on a system which uses 64k pages, it could. >> >> Okay. I got it. >> So, how about using PAGE_SIZE as ZRAM_LOGICAL_BLOCK_SIZE? >> Is there any reason to set 4096 to ZRAM_LOGICAL_BLOCK_SIZE, >> instead of setting PAGE_SIZE to ZRAM_LOGICAL_BLOCK_SIZE? >> > > ZRAM_LOGICAL_BLOCK_SIZE was introduced in commit 7b19b8d because the > block layer couldn't handle 64k logical block. Also, some filesytems > (including FAT IRC), can't cope with 64k block either. >
Okay. I will check it more.
Thanks for nice comment!!
|  |