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[216.228.121.143]) by mx.google.com with ESMTPS id k205si626065oih.182.2019.06.06.20.06.58 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 06 Jun 2019 20:06:59 -0700 (PDT) Received-SPF: pass (google.com: domain of jhubbard@nvidia.com designates 216.228.121.143 as permitted sender) client-ip=216.228.121.143; Authentication-Results: mx.google.com; dkim=pass header.i=@nvidia.com header.s=n1 header.b="rcX/eN6S"; spf=pass (google.com: domain of jhubbard@nvidia.com designates 216.228.121.143 as permitted sender) smtp.mailfrom=jhubbard@nvidia.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=nvidia.com Received: from hqpgpgate102.nvidia.com (Not Verified[216.228.121.13]) by hqemgate14.nvidia.com (using TLS: TLSv1.2, DES-CBC3-SHA) id ; Thu, 06 Jun 2019 20:06:56 -0700 Received: from hqmail.nvidia.com ([172.20.161.6]) by hqpgpgate102.nvidia.com (PGP Universal service); Thu, 06 Jun 2019 20:06:58 -0700 X-PGP-Universal: processed; by hqpgpgate102.nvidia.com on Thu, 06 Jun 2019 20:06:58 -0700 Received: from [10.110.48.28] (172.20.13.39) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Fri, 7 Jun 2019 03:06:53 +0000 Subject: Re: [PATCH v2 hmm 05/11] mm/hmm: Remove duplicate condition test before wait_event_timeout To: Jason Gunthorpe , Jerome Glisse , "Ralph Campbell" , CC: , , Andrea Arcangeli , , , Jason Gunthorpe References: <20190606184438.31646-1-jgg@ziepe.ca> <20190606184438.31646-6-jgg@ziepe.ca> X-Nvconfidentiality: public From: John Hubbard Message-ID: <86962e22-88b1-c1bf-d704-d5a5053fa100@nvidia.com> Date: Thu, 6 Jun 2019 20:06:52 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <20190606184438.31646-6-jgg@ziepe.ca> X-Originating-IP: [172.20.13.39] X-ClientProxiedBy: HQMAIL107.nvidia.com (172.20.187.13) To HQMAIL107.nvidia.com (172.20.187.13) Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: quoted-printable DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1559876816; bh=70o7ZS6CN7LiHClrr+qrAlqXgM2IDbvgx4VtZ9W6MfI=; h=X-PGP-Universal:Subject:To:CC:References:X-Nvconfidentiality:From: Message-ID:Date:User-Agent:MIME-Version:In-Reply-To: X-Originating-IP:X-ClientProxiedBy:Content-Type:Content-Language: Content-Transfer-Encoding; b=rcX/eN6SVVb8ntWY1bOCeo2lBWMdj/N0N59oEGCkUxTi+CQysb8+Bm72YdWdznjXv uMOqdy7CCjAssMyL0E+Wpqk7VGurL+Y48RwVXOiE8ewwA1U8PM/9NZJE3xkitfRbtm 2R0tTcKErsh4WABPJBiUUMm4qcT3D6UQGwZHfks5mqPWmj/hL5PzkvqZmoGIUzQXf3 h9jcXai0x0Nv32FWsJ/50DqS9x6531hNChV2FjPMMCXA0i+ZaV8RiLIfBNHoaTVury k8sBx3IJeGnHRXFDISxYSujNyNbyr19jEa+rGYPb4C2q0guYMp9a4Ef1nDI5HcNP4z RX+XUhHxNd0JQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 6/6/19 11:44 AM, Jason Gunthorpe wrote: > From: Jason Gunthorpe >=20 > The wait_event_timeout macro already tests the condition as its first > action, so there is no reason to open code another version of this, all > that does is skip the might_sleep() debugging in common cases, which is > not helpful. >=20 > Further, based on prior patches, we can no simplify the required conditio= n "now simplify" > test: > - If range is valid memory then so is range->hmm > - If hmm_release() has run then range->valid is set to false > at the same time as dead, so no reason to check both. > - A valid hmm has a valid hmm->mm. >=20 > Also, add the READ_ONCE for range->valid as there is no lock held here. >=20 > Signed-off-by: Jason Gunthorpe > Reviewed-by: J=C3=A9r=C3=B4me Glisse > --- > include/linux/hmm.h | 12 ++---------- > 1 file changed, 2 insertions(+), 10 deletions(-) >=20 > diff --git a/include/linux/hmm.h b/include/linux/hmm.h > index 4ee3acabe5ed22..2ab35b40992b24 100644 > --- a/include/linux/hmm.h > +++ b/include/linux/hmm.h > @@ -218,17 +218,9 @@ static inline unsigned long hmm_range_page_size(cons= t struct hmm_range *range) > static inline bool hmm_range_wait_until_valid(struct hmm_range *range, > unsigned long timeout) > { > - /* Check if mm is dead ? */ > - if (range->hmm =3D=3D NULL || range->hmm->dead || range->hmm->mm =3D=3D= NULL) { > - range->valid =3D false; > - return false; > - } > - if (range->valid) > - return true; > - wait_event_timeout(range->hmm->wq, range->valid || range->hmm->dead, > + wait_event_timeout(range->hmm->wq, range->valid, > msecs_to_jiffies(timeout)); > - /* Return current valid status just in case we get lucky */ > - return range->valid; > + return READ_ONCE(range->valid); Just to ensure that I actually understand the model: I'm assuming that the= =20 READ_ONCE is there solely to ensure that range->valid is read *after* the wait_event_timeout() returns. Is that correct? > } > =20 > /* >=20 In any case, it looks good, so: Reviewed-by: John Hubbard thanks, --=20 John Hubbard NVIDIA