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Message-ID: <Z6UJKTCkffZ93us5@google.com>
Date: Thu, 6 Feb 2025 19:10:33 +0000
From: Yosry Ahmed <yosry.ahmed@...ux.dev>
To: Kanchana P Sridhar <kanchana.p.sridhar@...el.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, hannes@...xchg.org,
nphamcs@...il.com, chengming.zhou@...ux.dev, usamaarif642@...il.com,
ryan.roberts@....com, 21cnbao@...il.com, akpm@...ux-foundation.org,
linux-crypto@...r.kernel.org, herbert@...dor.apana.org.au,
davem@...emloft.net, clabbe@...libre.com, ardb@...nel.org,
ebiggers@...gle.com, surenb@...gle.com, kristen.c.accardi@...el.com,
wajdi.k.feghali@...el.com, vinodh.gopal@...el.com
Subject: Re: [PATCH v6 15/16] mm: zswap: Compress batching with Intel IAA in
zswap_store() of large folios.
On Wed, Feb 05, 2025 at 11:21:01PM -0800, Kanchana P Sridhar wrote:
> zswap_compress_folio() is modified to detect if the pool's acomp_ctx has
> more than one "nr_reqs", which will be the case if the cpu onlining code
> has allocated multiple batching resources in the acomp_ctx. If so, it means
> compress batching can be used with a batch-size of "acomp_ctx->nr_reqs".
>
> If compress batching can be used, zswap_compress_folio() will invoke the
> newly added zswap_batch_compress() procedure to compress and store the
> folio in batches of "acomp_ctx->nr_reqs" pages.
>
> With Intel IAA, the iaa_crypto driver will compress each batch of pages in
> parallel in hardware.
>
> Hence, zswap_batch_compress() does the same computes for a batch, as
> zswap_compress() does for a page; and returns true if the batch was
> successfully compressed/stored, and false otherwise.
>
> If the pool does not support compress batching, or the folio has only one
> page, zswap_compress_folio() calls zswap_compress() for each individual
> page in the folio, as before.
>
> Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@...el.com>
> ---
> mm/zswap.c | 122 +++++++++++++++++++++++++++++++++++++++++++++++++----
> 1 file changed, 113 insertions(+), 9 deletions(-)
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 6563d12e907b..f1cba77eda62 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -985,10 +985,11 @@ static void acomp_ctx_put_unlock(struct crypto_acomp_ctx *acomp_ctx)
> mutex_unlock(&acomp_ctx->mutex);
> }
>
> +/* The per-cpu @acomp_ctx mutex should be locked/unlocked in the caller. */
Please use lockdep assertions rather than comments for internal locking rules.
> static bool zswap_compress(struct page *page, struct zswap_entry *entry,
> - struct zswap_pool *pool)
> + struct zswap_pool *pool,
> + struct crypto_acomp_ctx *acomp_ctx)
> {
> - struct crypto_acomp_ctx *acomp_ctx;
> struct scatterlist input, output;
> int comp_ret = 0, alloc_ret = 0;
> unsigned int dlen = PAGE_SIZE;
> @@ -998,7 +999,6 @@ static bool zswap_compress(struct page *page, struct zswap_entry *entry,
> gfp_t gfp;
> u8 *dst;
>
> - acomp_ctx = acomp_ctx_get_cpu_lock(pool);
> dst = acomp_ctx->buffers[0];
> sg_init_table(&input, 1);
> sg_set_page(&input, page, PAGE_SIZE, 0);
> @@ -1051,7 +1051,6 @@ static bool zswap_compress(struct page *page, struct zswap_entry *entry,
> else if (alloc_ret)
> zswap_reject_alloc_fail++;
>
> - acomp_ctx_put_unlock(acomp_ctx);
> return comp_ret == 0 && alloc_ret == 0;
> }
>
> @@ -1509,20 +1508,125 @@ static void shrink_worker(struct work_struct *w)
> * main API
> **********************************/
>
> +/* The per-cpu @acomp_ctx mutex should be locked/unlocked in the caller. */
> +static bool zswap_batch_compress(struct folio *folio,
> + long index,
> + unsigned int batch_size,
> + struct zswap_entry *entries[],
> + struct zswap_pool *pool,
> + struct crypto_acomp_ctx *acomp_ctx)
> +{
> + int comp_errors[ZSWAP_MAX_BATCH_SIZE] = { 0 };
> + unsigned int dlens[ZSWAP_MAX_BATCH_SIZE];
> + struct page *pages[ZSWAP_MAX_BATCH_SIZE];
> + unsigned int i, nr_batch_pages;
> + bool ret = true;
> +
> + nr_batch_pages = min((unsigned int)(folio_nr_pages(folio) - index), batch_size);
> +
> + for (i = 0; i < nr_batch_pages; ++i) {
> + pages[i] = folio_page(folio, index + i);
> + dlens[i] = PAGE_SIZE;
> + }
> +
> + /*
> + * Batch compress @nr_batch_pages. If IAA is the compressor, the
> + * hardware will compress @nr_batch_pages in parallel.
> + */
Please do not specifically mention IAA in zswap.c, as batching could be
supported in the future by other compressors.
> + ret = crypto_acomp_batch_compress(
> + acomp_ctx->reqs,
> + NULL,
> + pages,
> + acomp_ctx->buffers,
> + dlens,
> + comp_errors,
> + nr_batch_pages);
Does crypto_acomp_batch_compress() not require calling
crypto_wait_req()?
> +
> + if (ret) {
> + /*
> + * All batch pages were successfully compressed.
> + * Store the pages in zpool.
> + */
> + struct zpool *zpool = pool->zpool;
> + gfp_t gfp = __GFP_NORETRY | __GFP_NOWARN | __GFP_KSWAPD_RECLAIM;
> +
> + if (zpool_malloc_support_movable(zpool))
> + gfp |= __GFP_HIGHMEM | __GFP_MOVABLE;
> +
> + for (i = 0; i < nr_batch_pages; ++i) {
> + unsigned long handle;
> + char *buf;
> + int err;
> +
> + err = zpool_malloc(zpool, dlens[i], gfp, &handle);
> +
> + if (err) {
> + if (err == -ENOSPC)
> + zswap_reject_compress_poor++;
> + else
> + zswap_reject_alloc_fail++;
> +
> + ret = false;
> + break;
> + }
> +
> + buf = zpool_map_handle(zpool, handle, ZPOOL_MM_WO);
> + memcpy(buf, acomp_ctx->buffers[i], dlens[i]);
> + zpool_unmap_handle(zpool, handle);
> +
> + entries[i]->handle = handle;
> + entries[i]->length = dlens[i];
> + }
> + } else {
> + /* Some batch pages had compression errors. */
> + for (i = 0; i < nr_batch_pages; ++i) {
> + if (comp_errors[i]) {
> + if (comp_errors[i] == -ENOSPC)
> + zswap_reject_compress_poor++;
> + else
> + zswap_reject_compress_fail++;
> + }
> + }
> + }
This function is awfully close to zswap_compress(). It's essentially a
vectorized version and uses crypto_acomp_batch_compress() instead of
crypto_acomp_compress().
My questions are:
- Can we use crypto_acomp_batch_compress() for the non-batched case as
well to unify the code? Does it cause any regressions?
- If we have to use different compressions APIs, can we at least reuse
the rest of the code? We can abstract the compression call into a
helper that chooses the appropriate API based on the batch size. The
rest should be the same AFAICT.
> +
> + return ret;
> +}
> +
> static bool zswap_compress_folio(struct folio *folio,
> struct zswap_entry *entries[],
> struct zswap_pool *pool)
> {
> long index, nr_pages = folio_nr_pages(folio);
> + struct crypto_acomp_ctx *acomp_ctx;
> + unsigned int batch_size;
> + bool ret = true;
>
> - for (index = 0; index < nr_pages; ++index) {
> - struct page *page = folio_page(folio, index);
> + acomp_ctx = acomp_ctx_get_cpu_lock(pool);
> + batch_size = acomp_ctx->nr_reqs;
> +
> + if ((batch_size > 1) && (nr_pages > 1)) {
> + for (index = 0; index < nr_pages; index += batch_size) {
> +
> + if (!zswap_batch_compress(folio, index, batch_size,
> + &entries[index], pool, acomp_ctx)) {
> + ret = false;
> + goto unlock_acomp_ctx;
> + }
> + }
> + } else {
> + for (index = 0; index < nr_pages; ++index) {
> + struct page *page = folio_page(folio, index);
>
> - if (!zswap_compress(page, entries[index], pool))
> - return false;
> + if (!zswap_compress(page, entries[index], pool, acomp_ctx)) {
> + ret = false;
> + goto unlock_acomp_ctx;
> + }
> + }
> }
>
> - return true;
> +unlock_acomp_ctx:
> + acomp_ctx_put_unlock(acomp_ctx);
> + return ret;
> }
>
> /*
> --
> 2.27.0
>
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