Re: [PATCH 5/7] mm/zswap: refactor out __zswap_load()

[Nhat Pham]

On Wed, Dec 6, 2023 at 1:46 AM Chengming Zhou
<zhouchengming@xxxxxxxxxxxxx> 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).

I love this refactoring a lot :) No reason why we should duplicate the
decompression logic shared between load and writeback.

>
> Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
> ---
>  mm/zswap.c | 108 ++++++++++++++++++++++---------------------------------------
>  1 file changed, 39 insertions(+), 69 deletions(-)
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 999671dcb469..667b66a3911b 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -1380,6 +1380,42 @@ 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;
> +
> +       /* decompress */

nit: I guess all this function does is decompression right? Doesn't
seem like this comment is necessary anymore... But this is just
nitpicking.

> +       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);
> +       ret = crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait);
> +       dlen = acomp_ctx->req->dlen;
> +       mutex_unlock(acomp_ctx->mutex);
> +
> +       if (zpool_can_sleep_mapped(zpool))
> +               zpool_unmap_handle(zpool, entry->handle);
> +
> +       BUG_ON(ret);
> +       BUG_ON(dlen != PAGE_SIZE);
> +}
> +
>  /*********************************
>  * writeback code
>  **********************************/
> @@ -1401,23 +1437,12 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
>         swp_entry_t swpentry = entry->swpentry;
>         struct page *page;
>         struct mempolicy *mpol;
> -       struct scatterlist input, output;
> -       struct crypto_acomp_ctx *acomp_ctx;
> -       struct zpool *pool = zswap_find_zpool(entry);
>         bool page_was_allocated;
> -       u8 *src, *tmp = NULL;
> -       unsigned int dlen;
>         int ret;
>         struct writeback_control wbc = {
>                 .sync_mode = WB_SYNC_NONE,
>         };
>
> -       if (!zpool_can_sleep_mapped(pool)) {
> -               tmp = kmalloc(PAGE_SIZE, GFP_KERNEL);
> -               if (!tmp)
> -                       return -ENOMEM;
> -       }
> -

Sweet. Less allocation == more efficient + less failure case :)

>         /* try to allocate swap cache page */
>         mpol = get_task_policy(current);
>         page = __read_swap_cache_async(swpentry, GFP_KERNEL, mpol,
> @@ -1450,33 +1475,7 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
>         }
>         spin_unlock(&tree->lock);
>
> -       /* decompress */
> -       acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
> -       dlen = PAGE_SIZE;
> -
> -       src = zpool_map_handle(pool, entry->handle, ZPOOL_MM_RO);
> -       if (!zpool_can_sleep_mapped(pool)) {
> -               memcpy(tmp, src, entry->length);
> -               src = tmp;
> -               zpool_unmap_handle(pool, entry->handle);
> -       }
> -
> -       mutex_lock(acomp_ctx->mutex);
> -       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);
> -       ret = crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait);
> -       dlen = acomp_ctx->req->dlen;
> -       mutex_unlock(acomp_ctx->mutex);
> -
> -       if (!zpool_can_sleep_mapped(pool))
> -               kfree(tmp);
> -       else
> -               zpool_unmap_handle(pool, entry->handle);
> -
> -       BUG_ON(ret);
> -       BUG_ON(dlen != PAGE_SIZE);
> +       __zswap_load(entry, page);
>
>         /* page is up to date */
>         SetPageUptodate(page);
> @@ -1496,9 +1495,6 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
>         return ret;
>
>  fail:
> -       if (!zpool_can_sleep_mapped(pool))
> -               kfree(tmp);
> -
>         /*
>          * If we get here because the page is already in swapcache, a
>          * load may be happening concurrently. It is safe and okay to
> @@ -1755,11 +1751,7 @@ bool zswap_load(struct folio *folio)
>         struct page *page = &folio->page;
>         struct zswap_tree *tree = swap_zswap_tree(swp);
>         struct zswap_entry *entry;
> -       struct scatterlist input, output;
> -       struct crypto_acomp_ctx *acomp_ctx;
> -       unsigned int dlen = PAGE_SIZE;
> -       u8 *src, *dst;
> -       struct zpool *zpool;
> +       u8 *dst;
>         bool ret;
>
>         VM_WARN_ON_ONCE(!folio_test_locked(folio));
> @@ -1781,29 +1773,7 @@ bool zswap_load(struct folio *folio)
>                 goto stats;
>         }
>
> -       /* decompress */
> -       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);
> -       if (crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait))
> -               WARN_ON(1);
> -       mutex_unlock(acomp_ctx->mutex);
> -
> -       if (zpool_can_sleep_mapped(zpool))
> -               zpool_unmap_handle(zpool, entry->handle);
> -
> +       __zswap_load(entry, page);
>         ret = true;
>  stats:
>         count_vm_event(ZSWPIN);
>
> --
> b4 0.10.1

Can't find anything wrong with this patch, so:
Reviewed-by: Nhat Pham <nphamcs@xxxxxxxxx>