Re: [PATCH RFC 2/2] zram: support compression at the granularity of multi-pages

[Usama Arif <usamaarif642@gmail.com>]

On 22/10/2024 00:28, Barry Song wrote:
>> From: Tangquan Zheng <zhengtangquan@oppo.com>
>>
>> +static int zram_bvec_write_multi_pages(struct zram *zram, struct bio_vec *bvec,
>> +			   u32 index, int offset, struct bio *bio)
>> +{
>> +	if (is_multi_pages_partial_io(bvec))
>> +		return zram_bvec_write_multi_pages_partial(zram, bvec, index, offset, bio);
>> +	return zram_write_page(zram, bvec->bv_page, index);
>> +}
>> +

Hi Barry,

I started reviewing this series just to get a better idea if we can do something
similar for zswap. I haven't looked at zram code before so this might be a basic
question:
How would you end up in zram_bvec_write_multi_pages_partial if using zram for swap?

We only swapout whole folios. If ZCOMP_MULTI_PAGES_SIZE=64K, any folio smaller
than 64K will end up in zram_bio_write_page. Folios greater than or equal to 64K
would be dispatched by zram_bio_write_multi_pages to zram_bvec_write_multi_pages
in 64K chunks. So for e.g. 128K folio would end up calling zram_bvec_write_multi_pages
twice.

Or is this for the case when you are using zram not for swap? In that case, I probably
dont need to consider zram_bvec_write_multi_pages_partial write case for zswap.

Thanks,
Usama