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Message-ID: <SJ0PR11MB5678486805FB008DB5CF6EBCC94D2@SJ0PR11MB5678.namprd11.prod.outlook.com>
Date: Wed, 23 Oct 2024 02:01:06 +0000
From: "Sridhar, Kanchana P" <kanchana.p.sridhar@...el.com>
To: Yosry Ahmed <yosryahmed@...gle.com>, "ebiggers@...gle.com"
<ebiggers@...gle.com>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>, "hannes@...xchg.org"
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<vinodh.gopal@...el.com>, "Sridhar, Kanchana P"
<kanchana.p.sridhar@...el.com>
Subject: RE: [RFC PATCH v1 04/13] mm: zswap: zswap_compress()/decompress() can
submit, then poll an acomp_req.
Hi Yosry,
> -----Original Message-----
> From: Yosry Ahmed <yosryahmed@...gle.com>
> Sent: Tuesday, October 22, 2024 5:49 PM
> To: Sridhar, Kanchana P <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; Huang, Ying
> <ying.huang@...el.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; Accardi, Kristen C
> <kristen.c.accardi@...el.com>; zanussi@...nel.org; viro@...iv.linux.org.uk;
> brauner@...nel.org; jack@...e.cz; mcgrof@...nel.org; kees@...nel.org;
> joel.granados@...nel.org; bfoster@...hat.com; willy@...radead.org; linux-
> fsdevel@...r.kernel.org; Feghali, Wajdi K <wajdi.k.feghali@...el.com>; Gopal,
> Vinodh <vinodh.gopal@...el.com>
> Subject: Re: [RFC PATCH v1 04/13] mm: zswap:
> zswap_compress()/decompress() can submit, then poll an acomp_req.
>
> On Thu, Oct 17, 2024 at 11:41 PM Kanchana P Sridhar
> <kanchana.p.sridhar@...el.com> wrote:
> >
> > If the crypto_acomp has a poll interface registered, zswap_compress()
> > and zswap_decompress() will submit the acomp_req, and then poll() for a
> > successful completion/error status in a busy-wait loop. This allows an
> > asynchronous way to manage (potentially multiple) acomp_reqs without
> > the use of interrupts, which is supported in the iaa_crypto driver.
> >
> > This enables us to implement batch submission of multiple
> > compression/decompression jobs to the Intel IAA hardware accelerator,
> > which will process them in parallel; followed by polling the batch's
> > acomp_reqs for completion status.
> >
> > Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@...el.com>
> > ---
> > mm/zswap.c | 51 +++++++++++++++++++++++++++++++++++++++----------
> --
> > 1 file changed, 39 insertions(+), 12 deletions(-)
> >
> > diff --git a/mm/zswap.c b/mm/zswap.c
> > index f6316b66fb23..948c9745ee57 100644
> > --- a/mm/zswap.c
> > +++ b/mm/zswap.c
> > @@ -910,18 +910,34 @@ static bool zswap_compress(struct page *page,
> struct zswap_entry *entry,
> > acomp_request_set_params(acomp_ctx->req, &input, &output,
> PAGE_SIZE, dlen);
> >
> > /*
> > - * 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.
> > + * If the crypto_acomp provides an asynchronous poll() interface,
> > + * submit the descriptor and poll for a completion status.
> > + *
> > + * It maybe looks a little bit silly that we send an asynchronous
> > + * request, then wait for its completion in a busy-wait poll loop, or,
> > + * 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 zswap.
> > + * 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);
> > + if (acomp_ctx->acomp->poll) {
> > + comp_ret = crypto_acomp_compress(acomp_ctx->req);
> > + if (comp_ret == -EINPROGRESS) {
> > + do {
> > + comp_ret = crypto_acomp_poll(acomp_ctx->req);
> > + if (comp_ret && comp_ret != -EAGAIN)
> > + break;
> > + } while (comp_ret);
> > + }
> > + } else {
> > + comp_ret =
> crypto_wait_req(crypto_acomp_compress(acomp_ctx->req), &acomp_ctx-
> >wait);
> > + }
> > +
>
> Is Herbert suggesting that crypto_wait_req(crypto_acomp_compress(..))
> essentially do the poll internally for IAA, and hence this change can
> be dropped?
Yes, you're right. I plan to submit a v2 shortly with Herbert's suggestion.
Thanks,
Kanchana
>
> > dlen = acomp_ctx->req->dlen;
> > if (comp_ret)
> > goto unlock;
> > @@ -959,6 +975,7 @@ static void zswap_decompress(struct zswap_entry
> *entry, struct folio *folio)
> > struct scatterlist input, output;
> > struct crypto_acomp_ctx *acomp_ctx;
> > u8 *src;
> > + int ret;
> >
> > acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
> > mutex_lock(&acomp_ctx->mutex);
> > @@ -984,7 +1001,17 @@ static void zswap_decompress(struct
> zswap_entry *entry, struct folio *folio)
> > sg_init_table(&output, 1);
> > sg_set_folio(&output, folio, PAGE_SIZE, 0);
> > acomp_request_set_params(acomp_ctx->req, &input, &output, entry-
> >length, PAGE_SIZE);
> > - BUG_ON(crypto_wait_req(crypto_acomp_decompress(acomp_ctx-
> >req), &acomp_ctx->wait));
> > + if (acomp_ctx->acomp->poll) {
> > + ret = crypto_acomp_decompress(acomp_ctx->req);
> > + if (ret == -EINPROGRESS) {
> > + do {
> > + ret = crypto_acomp_poll(acomp_ctx->req);
> > + BUG_ON(ret && ret != -EAGAIN);
> > + } while (ret);
> > + }
> > + } else {
> > +
> BUG_ON(crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req),
> &acomp_ctx->wait));
> > + }
> > BUG_ON(acomp_ctx->req->dlen != PAGE_SIZE);
> > mutex_unlock(&acomp_ctx->mutex);
> >
> > --
> > 2.27.0
> >
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