lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  linux-cve-announce  PHC 
Open Source and information security mailing list archives
 
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <CAGsJ_4yUCQrGKQD-oxSAhyvJ+fY_KXUoiVBXE_i0jDAhWiNGzA@mail.gmail.com>
Date: Wed, 27 Dec 2023 14:24:41 +1300
From: Barry Song <21cnbao@...il.com>
To: Chengming Zhou <zhouchengming@...edance.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Seth Jennings <sjenning@...hat.com>, 
	Johannes Weiner <hannes@...xchg.org>, Vitaly Wool <vitaly.wool@...sulko.com>, 
	Nhat Pham <nphamcs@...il.com>, Chris Li <chriscli@...gle.com>, 
	Yosry Ahmed <yosryahmed@...gle.com>, Dan Streetman <ddstreet@...e.org>, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org, Chris Li <chrisl@...nel.org>
Subject: Re: [PATCH v4 2/6] mm/zswap: reuse dstmem when decompress

On Wed, Dec 27, 2023 at 4:56 AM Chengming Zhou
<zhouchengming@...edance.com> wrote:
>
> In the !zpool_can_sleep_mapped() case such as zsmalloc, we need to first
> copy the entry->handle memory to a temporary memory, which is allocated
> using kmalloc.
>
> Obviously we can reuse the per-compressor dstmem to avoid allocating
> every time, since it's percpu-compressor and protected in percpu mutex.

what is the benefit of this since we are actually increasing lock contention
by reusing this buffer between multiple compression and decompression
threads?

this mainly affects zsmalloc which can't sleep? do we have performance
data?

and it seems this patch is also negatively affecting z3fold and zbud.c
which actually don't need to allocate a tmp buffer.

>
> Reviewed-by: Nhat Pham <nphamcs@...il.com>
> Reviewed-by: Yosry Ahmed <yosryahmed@...gle.com>
> Acked-by: Chris Li <chrisl@...nel.org> (Google)
> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
> ---
>  mm/zswap.c | 44 ++++++++++++--------------------------------
>  1 file changed, 12 insertions(+), 32 deletions(-)
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 976f278aa507..6b872744e962 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -1417,19 +1417,13 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
>         struct crypto_acomp_ctx *acomp_ctx;
>         struct zpool *pool = zswap_find_zpool(entry);
>         bool page_was_allocated;
> -       u8 *src, *tmp = NULL;
> +       u8 *src;
>         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;
> -       }
> -
>         /* try to allocate swap cache page */
>         mpol = get_task_policy(current);
>         page = __read_swap_cache_async(swpentry, GFP_KERNEL, mpol,
> @@ -1465,15 +1459,15 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
>         /* decompress */
>         acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
>         dlen = PAGE_SIZE;
> +       mutex_lock(acomp_ctx->mutex);
>
>         src = zpool_map_handle(pool, entry->handle, ZPOOL_MM_RO);
>         if (!zpool_can_sleep_mapped(pool)) {
> -               memcpy(tmp, src, entry->length);
> -               src = tmp;
> +               memcpy(acomp_ctx->dstmem, src, entry->length);
> +               src = acomp_ctx->dstmem;
>                 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);
> @@ -1482,9 +1476,7 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
>         dlen = acomp_ctx->req->dlen;
>         mutex_unlock(acomp_ctx->mutex);
>
> -       if (!zpool_can_sleep_mapped(pool))
> -               kfree(tmp);
> -       else
> +       if (zpool_can_sleep_mapped(pool))
>                 zpool_unmap_handle(pool, entry->handle);
>
>         BUG_ON(ret);
> @@ -1508,9 +1500,6 @@ 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
> @@ -1771,7 +1760,7 @@ bool zswap_load(struct folio *folio)
>         struct zswap_entry *entry;
>         struct scatterlist input, output;
>         struct crypto_acomp_ctx *acomp_ctx;
> -       u8 *src, *dst, *tmp;
> +       u8 *src, *dst;
>         struct zpool *zpool;
>         unsigned int dlen;
>         bool ret;
> @@ -1796,26 +1785,19 @@ bool zswap_load(struct folio *folio)
>         }
>
>         zpool = zswap_find_zpool(entry);
> -       if (!zpool_can_sleep_mapped(zpool)) {
> -               tmp = kmalloc(entry->length, GFP_KERNEL);
> -               if (!tmp) {
> -                       ret = false;
> -                       goto freeentry;
> -               }
> -       }
>
>         /* decompress */
>         dlen = PAGE_SIZE;
> -       src = zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO);
> +       acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
> +       mutex_lock(acomp_ctx->mutex);
>
> +       src = zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO);
>         if (!zpool_can_sleep_mapped(zpool)) {
> -               memcpy(tmp, src, entry->length);
> -               src = tmp;
> +               memcpy(acomp_ctx->dstmem, src, entry->length);
> +               src = acomp_ctx->dstmem;
>                 zpool_unmap_handle(zpool, entry->handle);
>         }
>
> -       acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
> -       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);
> @@ -1826,15 +1808,13 @@ bool zswap_load(struct folio *folio)
>
>         if (zpool_can_sleep_mapped(zpool))
>                 zpool_unmap_handle(zpool, entry->handle);
> -       else
> -               kfree(tmp);
>
>         ret = true;
>  stats:
>         count_vm_event(ZSWPIN);
>         if (entry->objcg)
>                 count_objcg_event(entry->objcg, ZSWPIN);
> -freeentry:
> +
>         spin_lock(&tree->lock);
>         if (ret && zswap_exclusive_loads_enabled) {
>                 zswap_invalidate_entry(tree, entry);
>
> --
> b4 0.10.1
>

Powered by blists - more mailing lists