From: Huaisheng HS1 Ye <yehs1@lenovo.com>
To: Christian Borntraeger <borntraeger@de.ibm.com>,
"linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>,
"dan.j.williams@intel.com" <dan.j.williams@intel.com>
Cc: "axboe@kernel.dk" <axboe@kernel.dk>,
"linux-s390@vger.kernel.org" <linux-s390@vger.kernel.org>,
NingTing Cheng <chengnt@lenovo.com>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
"heiko.carstens@de.ibm.com" <heiko.carstens@de.ibm.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"willy@infradead.org" <willy@infradead.org>,
"bart.vanassche@wdc.com" <bart.vanassche@wdc.com>,
"viro@zeniv.linux.org.uk" <viro@zeniv.linux.org.uk>,
"gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
"schwidefsky@de.ibm.com" <schwidefsky@de.ibm.com>,
"jack@suse.cz" <jack@suse.cz>
Subject: RE: [External] Re: [PATCH 3/5] s390, dcssblk: Allow a NULL-kaddr to ->direct_access()
Date: Tue, 24 Jul 2018 09:46:43 +0000 [thread overview]
Message-ID: <TY2PR03MB3343901A038D3E3D836C438992550@TY2PR03MB3343.apcprd03.prod.outlook.com> (raw)
In-Reply-To: <192a9dac-921f-e222-3a7d-32d43679cd12@de.ibm.com>
From: Christian Borntraeger <borntraeger@de.ibm.com>
Sent: Tuesday, July 24, 2018 4:54 PM
> On 07/24/2018 10:45 AM, Huaisheng Ye wrote:
> > From: Huaisheng Ye <yehs1@lenovo.com>
> >
> > dcssblk_direct_access() needs to check the validity of second rank
> > pointer kaddr for NULL assignment. If kaddr equals to NULL, it
> > doesn't need to calculate the value.
> >
> > Signed-off-by: Huaisheng Ye <yehs1@lenovo.com>
> > ---
> > drivers/s390/block/dcssblk.c | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/s390/block/dcssblk.c b/drivers/s390/block/dcssblk.c
> > index 0a312e4..9c13dc5 100644
> > --- a/drivers/s390/block/dcssblk.c
> > +++ b/drivers/s390/block/dcssblk.c
> > @@ -915,7 +915,8 @@ static DEVICE_ATTR(save, S_IWUSR | S_IRUSR, dcssblk_save_show,
> > unsigned long dev_sz;
> >
> > dev_sz = dev_info->end - dev_info->start + 1;
> > - *kaddr = (void *) dev_info->start + offset;
> > + if (kaddr)
> > + *kaddr = (void *) dev_info->start + offset;
>
> 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.
Cheers,
Huaisheng Ye
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next prev parent reply other threads:[~2018-07-24 9:47 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-24 8:45 [PATCH 0/5] Do not request a pointer kaddr when not required Huaisheng Ye
2018-07-24 8:45 ` [PATCH 1/5] libnvdimm, pmem: Allow a NULL-kaddr to ->direct_access() Huaisheng Ye
2018-07-24 8:45 ` [PATCH 2/5] tools/testing/nvdimm: " Huaisheng Ye
2018-07-24 8:45 ` [PATCH 3/5] s390, dcssblk: " Huaisheng Ye
2018-07-24 8:53 ` Christian Borntraeger
2018-07-24 9:46 ` Huaisheng HS1 Ye [this message]
2018-07-24 11:16 ` [External] " Christian Borntraeger
2018-07-24 14:28 ` Huaisheng HS1 Ye
2018-07-24 8:45 ` [PATCH 4/5] filesystem-dax: Do not request a pointer kaddr when not required Huaisheng Ye
2018-07-24 8:45 ` [PATCH 5/5] dax/super: " Huaisheng Ye
2018-07-24 14:50 ` [PATCH 0/5] " Ross Zwisler
2018-07-24 15:41 ` [External] " Huaisheng HS1 Ye
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