Re: [RFC PATCH v1 04/13] mm: zswap: zswap_compress()/decompress() can submit, then poll an acomp_req.

[Yosry Ahmed]

On Thu, Oct 17, 2024 at 11:41 PM Kanchana P Sridhar
<kanchana.p.sridhar@xxxxxxxxx> wrote:
>
> If the crypto_acomp has a poll interface registered, zswap_compress()
> and zswap_decompress() will submit the acomp_req, and then poll() for a
> successful completion/error status in a busy-wait loop. This allows an
> asynchronous way to manage (potentially multiple) acomp_reqs without
> the use of interrupts, which is supported in the iaa_crypto driver.
>
> This enables us to implement batch submission of multiple
> compression/decompression jobs to the Intel IAA hardware accelerator,
> which will process them in parallel; followed by polling the batch's
> acomp_reqs for completion status.
>
> Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@xxxxxxxxx>
> ---
>  mm/zswap.c | 51 +++++++++++++++++++++++++++++++++++++++------------
>  1 file changed, 39 insertions(+), 12 deletions(-)
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index f6316b66fb23..948c9745ee57 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -910,18 +910,34 @@ static bool zswap_compress(struct page *page, struct zswap_entry *entry,
>         acomp_request_set_params(acomp_ctx->req, &input, &output, PAGE_SIZE, dlen);
>
>         /*
> -        * it maybe looks a little bit silly that we send an asynchronous request,
> -        * then wait for its completion synchronously. This makes the process look
> -        * synchronous in fact.
> -        * Theoretically, acomp supports users send multiple acomp requests in one
> -        * acomp instance, then get those requests done simultaneously. but in this
> -        * case, zswap actually does store and load page by page, there is no
> -        * existing method to send the second page before the first page is done
> -        * in one thread doing zwap.
> -        * but in different threads running on different cpu, we have different
> -        * acomp instance, so multiple threads can do (de)compression in parallel.
> +        * If the crypto_acomp provides an asynchronous poll() interface,
> +        * submit the descriptor and poll for a completion status.
> +        *
> +        * It maybe looks a little bit silly that we send an asynchronous
> +        * request, then wait for its completion in a busy-wait poll loop, or,
> +        * synchronously. This makes the process look synchronous in fact.
> +        * Theoretically, acomp supports users send multiple acomp requests in
> +        * one acomp instance, then get those requests done simultaneously.
> +        * But in this case, zswap actually does store and load page by page,
> +        * there is no existing method to send the second page before the
> +        * first page is done in one thread doing zswap.
> +        * But in different threads running on different cpu, we have different
> +        * acomp instance, so multiple threads can do (de)compression in
> +        * parallel.
>          */
> -       comp_ret = crypto_wait_req(crypto_acomp_compress(acomp_ctx->req), &acomp_ctx->wait);
> +       if (acomp_ctx->acomp->poll) {
> +               comp_ret = crypto_acomp_compress(acomp_ctx->req);
> +               if (comp_ret == -EINPROGRESS) {
> +                       do {
> +                               comp_ret = crypto_acomp_poll(acomp_ctx->req);
> +                               if (comp_ret && comp_ret != -EAGAIN)
> +                                       break;
> +                       } while (comp_ret);
> +               }
> +       } else {
> +               comp_ret = crypto_wait_req(crypto_acomp_compress(acomp_ctx->req), &acomp_ctx->wait);
> +       }
> +

Is Herbert suggesting that crypto_wait_req(crypto_acomp_compress(..))
essentially do the poll internally for IAA, and hence this change can
be dropped?

>         dlen = acomp_ctx->req->dlen;
>         if (comp_ret)
>                 goto unlock;
> @@ -959,6 +975,7 @@ static void zswap_decompress(struct zswap_entry *entry, struct folio *folio)
>         struct scatterlist input, output;
>         struct crypto_acomp_ctx *acomp_ctx;
>         u8 *src;
> +       int ret;
>
>         acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
>         mutex_lock(&acomp_ctx->mutex);
> @@ -984,7 +1001,17 @@ static void zswap_decompress(struct zswap_entry *entry, struct folio *folio)
>         sg_init_table(&output, 1);
>         sg_set_folio(&output, folio, PAGE_SIZE, 0);
>         acomp_request_set_params(acomp_ctx->req, &input, &output, entry->length, PAGE_SIZE);
> -       BUG_ON(crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait));
> +       if (acomp_ctx->acomp->poll) {
> +               ret = crypto_acomp_decompress(acomp_ctx->req);
> +               if (ret == -EINPROGRESS) {
> +                       do {
> +                               ret = crypto_acomp_poll(acomp_ctx->req);
> +                               BUG_ON(ret && ret != -EAGAIN);
> +                       } while (ret);
> +               }
> +       } else {
> +               BUG_ON(crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait));
> +       }
>         BUG_ON(acomp_ctx->req->dlen != PAGE_SIZE);
>         mutex_unlock(&acomp_ctx->mutex);
>
> --
> 2.27.0
>