linux-kernel - Re: [PATCH 2/3] mm/zswap: remove the memcpy if acomp is not asynchronous

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Message-ID: <CAKEwX=MDNuW72OS81mXgAKMdBnT2MCTGJtXx8cgMLh=J_Nv-ew@mail.gmail.com>
Date: Wed, 3 Jan 2024 16:38:41 -0800
From: Nhat Pham <nphamcs@...il.com>
To: Barry Song <21cnbao@...il.com>
Cc: herbert@...dor.apana.org.au, davem@...emloft.net, 
	akpm@...ux-foundation.org, ddstreet@...e.org, sjenning@...hat.com, 
	vitaly.wool@...sulko.com, linux-crypto@...r.kernel.org, chriscli@...gle.com, 
	chrisl@...nel.org, hannes@...xchg.org, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org, yosryahmed@...gle.com, zhouchengming@...edance.com, 
	Barry Song <v-songbaohua@...o.com>
Subject: Re: [PATCH 2/3] mm/zswap: remove the memcpy if acomp is not asynchronous

On Wed, Jan 3, 2024 at 1:50 AM Barry Song <21cnbao@...il.com> wrote:
>
> From: Barry Song <v-songbaohua@...o.com>
>
> Most compressors are actually CPU-based and won't sleep during
> compression and decompression. We should remove the redundant
> memcpy for them.
>
> Signed-off-by: Barry Song <v-songbaohua@...o.com>
> Tested-by: Chengming Zhou <zhouchengming@...edance.com>

nit: it might help to include the test numbers in the changelog in
this patch here too. Save a couple of clicks to dig out the original
patch cover for the numbers :)

> ---
>  mm/zswap.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index ca25b676048e..36898614ebcc 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -168,6 +168,7 @@ struct crypto_acomp_ctx {
>         struct crypto_wait wait;
>         u8 *buffer;
>         struct mutex mutex;
> +       bool is_async; /* if acomp can sleep */

nit: seems like this comment isn't necessary. is_async is pretty
self-explanatory to me. But definitely not a show stopper tho :)

>  };
>
>  /*
> @@ -716,6 +717,7 @@ static int zswap_cpu_comp_prepare(unsigned int cpu, struct hlist_node *node)
>                 goto acomp_fail;
>         }
>         acomp_ctx->acomp = acomp;
> +       acomp_ctx->is_async = acomp_is_async(acomp);
>
>         req = acomp_request_alloc(acomp_ctx->acomp);
>         if (!req) {
> @@ -1370,7 +1372,7 @@ static void __zswap_load(struct zswap_entry *entry, struct page *page)
>         mutex_lock(&acomp_ctx->mutex);
>
>         src = zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO);
> -       if (!zpool_can_sleep_mapped(zpool)) {
> +       if (acomp_ctx->is_async && !zpool_can_sleep_mapped(zpool)) {
>                 memcpy(acomp_ctx->buffer, src, entry->length);
>                 src = acomp_ctx->buffer;
>                 zpool_unmap_handle(zpool, entry->handle);
> @@ -1384,7 +1386,7 @@ static void __zswap_load(struct zswap_entry *entry, struct page *page)
>         BUG_ON(acomp_ctx->req->dlen != PAGE_SIZE);
>         mutex_unlock(&acomp_ctx->mutex);
>
> -       if (zpool_can_sleep_mapped(zpool))
> +       if (!acomp_ctx->is_async || zpool_can_sleep_mapped(zpool))
>                 zpool_unmap_handle(zpool, entry->handle);
>  }
>
> --
> 2.34.1
>

The zswap side looks good to me. I don't have expertise/authority to
ack the crypto API change (but FWIW it LGTM too based on a cursory
code read).
Reviewed-by: Nhat Pham <nphamcs@...il.com>