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Message-ID: <CAGsJ_4xH7aU37w03-4MSJs7Bik6pShLfad8RY8TSzj37AcGwDg@mail.gmail.com>
Date: Fri, 29 Aug 2025 11:31:21 +0800
From: Barry Song <21cnbao@...il.com>
To: "Sridhar, Kanchana P" <kanchana.p.sridhar@...el.com>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-mm@...ck.org" <linux-mm@...ck.org>,
"hannes@...xchg.org" <hannes@...xchg.org>, "yosry.ahmed@...ux.dev" <yosry.ahmed@...ux.dev>,
"nphamcs@...il.com" <nphamcs@...il.com>, "chengming.zhou@...ux.dev" <chengming.zhou@...ux.dev>,
"usamaarif642@...il.com" <usamaarif642@...il.com>, "ryan.roberts@....com" <ryan.roberts@....com>,
"ying.huang@...ux.alibaba.com" <ying.huang@...ux.alibaba.com>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
"senozhatsky@...omium.org" <senozhatsky@...omium.org>,
"linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
"herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>, "davem@...emloft.net" <davem@...emloft.net>,
"clabbe@...libre.com" <clabbe@...libre.com>, "ardb@...nel.org" <ardb@...nel.org>,
"ebiggers@...gle.com" <ebiggers@...gle.com>, "surenb@...gle.com" <surenb@...gle.com>,
"Accardi, Kristen C" <kristen.c.accardi@...el.com>, "Gomes, Vinicius" <vinicius.gomes@...el.com>,
"Feghali, Wajdi K" <wajdi.k.feghali@...el.com>, "Gopal, Vinodh" <vinodh.gopal@...el.com>
Subject: Re: [PATCH v11 24/24] mm: zswap: Batched zswap_compress() with
compress batching of large folios.
On Fri, Aug 29, 2025 at 11:05 AM Sridhar, Kanchana P
<kanchana.p.sridhar@...el.com> wrote:
>
>
> > -----Original Message-----
> > From: Barry Song <21cnbao@...il.com>
> > Sent: Thursday, August 28, 2025 4:54 PM
> > To: Sridhar, Kanchana P <kanchana.p.sridhar@...el.com>
> > Cc: linux-kernel@...r.kernel.org; linux-mm@...ck.org;
> > hannes@...xchg.org; yosry.ahmed@...ux.dev; nphamcs@...il.com;
> > chengming.zhou@...ux.dev; usamaarif642@...il.com;
> > ryan.roberts@....com; ying.huang@...ux.alibaba.com; akpm@...ux-
> > foundation.org; senozhatsky@...omium.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; Accardi, Kristen C <kristen.c.accardi@...el.com>;
> > Gomes, Vinicius <vinicius.gomes@...el.com>; Feghali, Wajdi K
> > <wajdi.k.feghali@...el.com>; Gopal, Vinodh <vinodh.gopal@...el.com>
> > Subject: Re: [PATCH v11 24/24] mm: zswap: Batched zswap_compress() with
> > compress batching of large folios.
> >
> > > +static bool zswap_compress(struct folio *folio, long start, unsigned int
> > nr_pages,
> > > + struct zswap_entry *entries[], struct zswap_pool *pool,
> > > + int node_id)
> > > {
> > > struct crypto_acomp_ctx *acomp_ctx;
> > > struct scatterlist input, output;
> > > - int comp_ret = 0, alloc_ret = 0;
> > > - unsigned int dlen = PAGE_SIZE;
> > > - unsigned long handle;
> > > - struct zpool *zpool;
> > > + struct zpool *zpool = pool->zpool;
> > > +
> > > + unsigned int dlens[ZSWAP_MAX_BATCH_SIZE];
> > > + int errors[ZSWAP_MAX_BATCH_SIZE];
> > > +
> > > + unsigned int nr_comps = min(nr_pages, pool->compr_batch_size);
> > > + unsigned int i, j;
> > > + int err;
> > > gfp_t gfp;
> > > - u8 *dst;
> > > +
> > > + gfp = GFP_NOWAIT | __GFP_NORETRY | __GFP_HIGHMEM |
> > __GFP_MOVABLE;
> > >
> > > acomp_ctx = raw_cpu_ptr(pool->acomp_ctx);
> > >
> > > mutex_lock(&acomp_ctx->mutex);
> > >
> > > - dst = acomp_ctx->buffers[0];
> > > - sg_init_table(&input, 1);
> > > - sg_set_page(&input, page, PAGE_SIZE, 0);
> > > -
> > > /*
> > > - * We need PAGE_SIZE * 2 here since there maybe over-compression
> > case,
> > > - * and hardware-accelerators may won't check the dst buffer size, so
> > > - * giving the dst buffer with enough length to avoid buffer overflow.
> > > + * Note:
> > > + * [i] refers to the incoming batch space and is used to
> > > + * index into the folio pages, @entries and @errors.
> > > */
> > > - sg_init_one(&output, dst, PAGE_SIZE * 2);
> > > - acomp_request_set_params(acomp_ctx->req, &input, &output,
> > PAGE_SIZE, dlen);
> > > + for (i = 0; i < nr_pages; i += nr_comps) {
> > > + if (nr_comps == 1) {
> > > + sg_init_table(&input, 1);
> > > + sg_set_page(&input, folio_page(folio, start + i), PAGE_SIZE, 0);
> > >
> > > - /*
> > > - * it maybe looks a little bit silly that we send an asynchronous request,
> > > - * then wait for its completion synchronously. This makes the process
> > look
> > > - * synchronous in fact.
> > > - * Theoretically, acomp supports users send multiple acomp requests in
> > one
> > > - * acomp instance, then get those requests done simultaneously. but in
> > this
> > > - * case, zswap actually does store and load page by page, there is no
> > > - * existing method to send the second page before the first page is
> > done
> > > - * in one thread doing zwap.
> > > - * but in different threads running on different cpu, we have different
> > > - * acomp instance, so multiple threads can do (de)compression in
> > parallel.
> > > - */
> > > - comp_ret = crypto_wait_req(crypto_acomp_compress(acomp_ctx-
> > >req), &acomp_ctx->wait);
> > > - dlen = acomp_ctx->req->dlen;
> > > - if (comp_ret)
> > > - goto unlock;
> > > + /*
> > > + * We need PAGE_SIZE * 2 here since there maybe over-
> > compression case,
> > > + * and hardware-accelerators may won't check the dst buffer
> > size, so
> > > + * giving the dst buffer with enough length to avoid buffer
> > overflow.
> > > + */
> > > + sg_init_one(&output, acomp_ctx->buffers[0], PAGE_SIZE * 2);
> > > + acomp_request_set_params(acomp_ctx->req, &input,
> > > + &output, PAGE_SIZE, PAGE_SIZE);
> > > +
> > > + errors[i] =
> > crypto_wait_req(crypto_acomp_compress(acomp_ctx->req),
> > > + &acomp_ctx->wait);
> > > + if (unlikely(errors[i]))
> > > + goto compress_error;
> > > +
> > > + dlens[i] = acomp_ctx->req->dlen;
> > > + } else {
> > > + struct page *pages[ZSWAP_MAX_BATCH_SIZE];
> > > + unsigned int k;
> > > +
> > > + for (k = 0; k < nr_pages; ++k)
> > > + pages[k] = folio_page(folio, start + k);
> > > +
> > > + struct swap_batch_comp_data batch_comp_data = {
> > > + .pages = pages,
> > > + .dsts = acomp_ctx->buffers,
> > > + .dlens = dlens,
> > > + .errors = errors,
> > > + .nr_comps = nr_pages,
> > > + };
> >
> > Why would this work given that nr_pages might be larger than
> > pool->compr_batch_size?
>
> You mean the batching call? For batching compressors, nr_pages
> is always <= pool->batch_size. For batching compressors, pool->batch_size
> is the pool->compr_batch_size.
I’m actually confused that this feels inconsistent with the earlier
unsigned int nr_comps = min(nr_pages, pool->compr_batch_size);
So why not just use nr_comps instead?
>
> >
> > unsigned int nr_comps = min(nr_pages, pool->compr_batch_size);
> >
> > So this actually doesn’t happen unless pool->compr_batch_size == 1,
> > but the code is confusing, right?
> >
> > > +
> > > + acomp_ctx->req->kernel_data = &batch_comp_data;
> >
> > Can you actually pass a request larger than pool->compr_batch_size
> > to the crypto driver?
>
> Clarification above..
>
> >
> > By the way, swap_batch_comp_data seems like a poor name. Why should
> > crypto drivers know anything about swap_? kernel_data isn’t ideal either;
> > maybe batch_data would be better ?
>
> This will be changing in v12 to use an SG list based on Herbert's suggestions.
>
Cool. Thanks!
Thanks
Barry
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