> > -----Original Message----- > > From: linux-kernel-owner@xxxxxxxxxxxxxxx > > [mailto:linux-kernel-owner@xxxxxxxxxxxxxxx] On Behalf Of Herbert Xu > > Sent: Friday, June 26, 2020 7:20 PM > > To: Song Bao Hua (Barry Song) <song.bao.hua@xxxxxxxxxxxxx> > > Cc: akpm@xxxxxxxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx; > > linux-kernel@xxxxxxxxxxxxxxx; Linuxarm <linuxarm@xxxxxxxxxx>; Luis > > Claudio R . Goncalves <lgoncalv@xxxxxxxxxx>; Sebastian Andrzej Siewior > > <bigeasy@xxxxxxxxxxxxx>; David S . Miller <davem@xxxxxxxxxxxxx>; > > Mahipal Challa <mahipalreddy2006@xxxxxxxxx>; Seth Jennings > > <sjenning@xxxxxxxxxx>; Dan Streetman <ddstreet@xxxxxxxx>; Vitaly Wool > > <vitaly.wool@xxxxxxxxxxxx>; Wangzhou (B) <wangzhou1@xxxxxxxxxxxxx>; > > Colin Ian King <colin.king@xxxxxxxxxxxxx> > > Subject: Re: [PATCH v3] mm/zswap: move to use crypto_acomp API for > > hardware acceleration > > > > On Fri, Jun 26, 2020 at 07:09:03PM +1200, Barry Song wrote: > > > > > > + mutex_lock(&acomp_ctx->mutex); > > > + > > > + src = kmap(page); > > > + dst = acomp_ctx->dstmem; > > > + sg_init_one(&input, src, PAGE_SIZE); > > > + /* zswap_dstmem is of size (PAGE_SIZE * 2). Reflect same in sg_list */ > > > + sg_init_one(&output, dst, PAGE_SIZE * 2); > > > + acomp_request_set_params(acomp_ctx->req, &input, &output, > > PAGE_SIZE, dlen); > > > + ret = crypto_wait_req(crypto_acomp_compress(acomp_ctx->req), > > &acomp_ctx->wait); > > > + dlen = acomp_ctx->req->dlen; > > > + kunmap(page); > > > > Waiting on an async request like this is just silly. This defeats the > > whole purpose of having a fallback. > > For this zswap case and for this moment, it is probably not. > As for this case, there are no two parallel (de)compressions which can be done > in parallel in a single (de)compressor instance. > The original zswap code is doing all compression/decompression in atomic > context. > Right now, to use acomp api, the patch has moved to sleep-able context. > > However, compression/decompression can be done in parallel in different > instances of acomp, also different cpus. > > If we want to do multiple (de)compressions simultaneously in one acomp > instance by callbacks, it will ask a large changes in zswap.c not only using the > new APIs. I think we can only achieve the ideal goal step by step. On the other hand, I also don't think mm/frontswap.c supports async store. It is pretty much a sync operation to call store callback of frontswap for every single page: int __frontswap_store(struct page *page) { ... /* Try to store in each implementation, until one succeeds. */ for_each_frontswap_ops(ops) { ret = ops->store(type, offset, page); if (!ret) /* successful store */ break; } ... if (frontswap_writethrough_enabled) /* report failure so swap also writes to swap device */ ret = -1; return ret; } If we don't want to execute a sync wait in zswap, a lot of things need changes, not only zswap. > > > > > Cheers, > > -- > > Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> Home Page: > > http://gondor.apana.org.au/~herbert/ > > PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt > > -barry Thanks Barry
