Re: [PATCH v4] zram: Implement multi-page write-back

Sergey Senozhatsky
2025-11-10T04:49:32Z

On (25/11/06 09:49), Yuwen Chen wrote:
> For block devices, sequential write performance is significantly
> better than random write. Currently, zram's write-back function
> only supports single-page operations, which fails to leverage
> the sequential write advantage and leads to suboptimal performance.

As a side note:
You almost never do sequential writes to the backing device. The
thing is, e.g. when zram is used as swap, page faults happen randomly
and free up (slot-free) random page-size chunks (so random bits in
zram->bitmap become clear), which then get overwritten (zram simply
picks the first available bit from zram->bitmap) during next writeback.
There is nothing sequential about that, in systems with sufficiently
large uptime and sufficiently frequent writeback/readback events
writeback bitmap becomes sparse, which results in random IO, so your
test tests an ideal case that almost never happens in practice.