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

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Date:   Thu, 14 Dec 2023 22:45:22 +0800
From:   Chengming Zhou <zhouchengming@...edance.com>
To:     Yosry Ahmed <yosryahmed@...gle.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 2023/12/14 08:52, Yosry Ahmed wrote:
> 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.
> 

Ok, will put it first.

>> ---
>>  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.

Ok, thanks!