linux-kernel - RE: [External] Re: [PATCH 3/5] s390, dcssblk: Allow a NULL-kaddr to ->direct

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Message-ID: <TY2PR03MB3343CC5CD32DBD527DABFDE592550@TY2PR03MB3343.apcprd03.prod.outlook.com>
Date:   Tue, 24 Jul 2018 14:28:23 +0000
From:   Huaisheng HS1 Ye <yehs1@...ovo.com>
To:     Christian Borntraeger <borntraeger@...ibm.com>
CC:     "ross.zwisler@...ux.intel.com" <ross.zwisler@...ux.intel.com>,
        "willy@...radead.org" <willy@...radead.org>,
        "vishal.l.verma@...el.com" <vishal.l.verma@...el.com>,
        "dave.jiang@...el.com" <dave.jiang@...el.com>,
        "schwidefsky@...ibm.com" <schwidefsky@...ibm.com>,
        "heiko.carstens@...ibm.com" <heiko.carstens@...ibm.com>,
        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "bart.vanassche@....com" <bart.vanassche@....com>,
        "jack@...e.cz" <jack@...e.cz>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        NingTing Cheng <chengnt@...ovo.com>,
        Huaisheng Ye <yehs2007@...o.com>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>
Subject: RE: [External] Re: [PATCH 3/5] s390, dcssblk: Allow a NULL-kaddr to
 ->direct_access()

From: Christian Borntraeger <borntraeger@...ibm.com>
Sent: Tuesday, July 24, 2018 7:16 PM
> >> So you are trading of a load + add (dev_info->start should be cache hot) against a
> >> compare+branch . Not sure that this is always a win.
> >
> > Hmm...the calculation process of pfn is more complicated than kaddr. I think you agree to
> check pfn but not sure kaddr, right?
> > From the logical consistency of code, I think it shall be better to give pfn and kaddr similar
> treatment.
> 
> Reading it again, its more that I do not like the patch description. It reads
> like an optimization, (and I think it is not) but it should rather read more
> like "with an upcoming change kaddr can be NULL" or so.

Thanks for suggestion, I will reword the patch description during next submission.
Does the patch itself need to be modified? If has, any suggestion is welcome.

Cheers,
Huaisheng Ye