Re: [PATCH v5 02/12] crypto: acomp - Define new interfaces for compress/decompress batching.

[Yosry Ahmed]

On Tue, Jan 7, 2025 at 5:39 PM Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> wrote:
>
> On Mon, Jan 06, 2025 at 07:10:53PM -0800, Yosry Ahmed wrote:
> >
> > The main problem is memory usage. Zswap needs a PAGE_SIZE*2-sized
> > buffer for each request on each CPU. We preallocate these buffers to
> > avoid trying to allocate this much memory in the reclaim path (i.e.
> > potentially allocating two pages to reclaim one).
>
> What if we allowed each acomp request to take a whole folio?
> That would mean you'd only need to allocate one request per
> folio, regardless of how big it is.

Hmm this means we need to allocate a single request instead of N
requests, but the source of overhead is the output buffers not the
requests. We need PAGE_SIZE*2 for each page in the folio in the output
buffer on each CPU. Preallocating this unnecessarily adds up to a lot
of memory.

Did I miss something?

>
> Eric, we could do something similar with ahash.  Allow the
> user to supply a folio (or scatterlist entry) instead of a
> single page, and then cut it up based on a unit-size supplied
> by the user (e.g., 512 bytes for sector-based users).  That
> would mean just a single request object as long as your input
> is a folio or something similar.
>
> Is this something that you could use in fs/verity? You'd still
> need to allocate enough memory to store the output hashes.
>
> Cheers,
> --
> Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
> Home Page: http://gondor.apana.org.au/~herbert/
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>