Re: [PATCH 06/10] Block discard support

Jens Axboe
2010-08-10T02:23:38Z

On 08/09/2010 03:03 PM, Pekka Enberg wrote:
> On Mon, Aug 9, 2010 at 8:26 PM, Nitin Gupta <ngupta@vflare.org> wrote:
>> The 'discard' bio discard request provides information to
>> zram disks regarding blocks which are no longer in use by
>> filesystem. This allows freeing memory allocated for such
>> blocks.
>>
>> When zram devices are used as swap disks, we already have
>> a callback (block_device_operations->swap_slot_free_notify).
>> So, the discard support is useful only when used as generic
>> (non-swap) disk.
>>
>> Signed-off-by: Nitin Gupta <ngupta@vflare.org>
>
> Lets CC fsdevel and Jens for this.

Looks OK from a quick look. One comment, though:

>> +static void zram_discard(struct zram *zram, struct bio *bio)
>> +{
>> + size_t bytes = bio->bi_size;
>> + sector_t sector = bio->bi_sector;
>> +
>> + while (bytes >= PAGE_SIZE) {
>> + zram_free_page(zram, sector >> SECTORS_PER_PAGE_SHIFT);
>> + sector += PAGE_SIZE >> SECTOR_SHIFT;
>> + bytes -= PAGE_SIZE;
>> + }
>> +
>> + bio_endio(bio, 0);
>> +}
>> +

So freeing the page here will guarantee zeroed return on read?
And since you set PAGE_SIZE as the discard granularity, the above loop
could be coded more readable with the knowledge that ->bi_size is always
a multiple of the page size.

--
Jens Axboe

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