linux-kernel - Re: [PATCH 3/5] mm/zswap: refactor out __zswap

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Date:   Wed, 13 Dec 2023 16:52:13 -0800
From:   Yosry Ahmed <yosryahmed@...gle.com>
To:     Chengming Zhou <zhouchengming@...edance.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Nhat Pham <nphamcs@...il.com>, Chris Li <chriscli@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Seth Jennings <sjenning@...hat.com>,
        Dan Streetman <ddstreet@...e.org>,
        Vitaly Wool <vitaly.wool@...sulko.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 3/5] mm/zswap: refactor out __zswap_load()

On Tue, Dec 12, 2023 at 8:18 PM Chengming Zhou
<zhouchengming@...edance.com> wrote:
>
> The zswap_load() and zswap_writeback_entry() have the same part that
> decompress the data from zswap_entry to page, so refactor out the
> common part as __zswap_load(entry, page).
>
> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
> Reviewed-by: Nhat Pham <nphamcs@...il.com>

On a second look, there a few nits here.

First I think it makes more sense to move this refactoring ahead of
reusing destmem. Right now, we add the destmem reuse to zswap_load()
only, then we do the refactor and zswap_writeback_entry() gets it
automatically, so there is a slight change coming to
zswap_writeback_entry() hidden in the refactoring patch.

Let's refactor out __zswap_load() first, then reuse destmem in it.

> ---
>  mm/zswap.c | 107 ++++++++++++++++++++++---------------------------------------
>  1 file changed, 38 insertions(+), 69 deletions(-)
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index fa186945010d..2f095c919a5c 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -1392,6 +1392,41 @@ static int zswap_enabled_param_set(const char *val,
>         return ret;
>  }
>
> +static void __zswap_load(struct zswap_entry *entry, struct page *page)
> +{
> +       struct scatterlist input, output;
> +       unsigned int dlen = PAGE_SIZE;
> +       struct crypto_acomp_ctx *acomp_ctx;
> +       struct zpool *zpool;
> +       u8 *src;
> +       int ret;
> +
> +       acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
> +       mutex_lock(acomp_ctx->mutex);
> +
> +       zpool = zswap_find_zpool(entry);
> +       src = zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO);
> +       if (!zpool_can_sleep_mapped(zpool)) {
> +               memcpy(acomp_ctx->dstmem, src, entry->length);
> +               src = acomp_ctx->dstmem;
> +               zpool_unmap_handle(zpool, entry->handle);
> +       }
> +
> +       sg_init_one(&input, src, entry->length);
> +       sg_init_table(&output, 1);
> +       sg_set_page(&output, page, PAGE_SIZE, 0);
> +       acomp_request_set_params(acomp_ctx->req, &input, &output, entry->length, dlen);

We should pass PAGE_SIZE here directly, BUG_ON(acomp_ctx->req->dlen)
below, and remove the dlen variable.

> +       ret = crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait);

We should just BUG_ON() here directly an remove the ret variable.