linux-kernel - RE: [External] Re: [PATCH 0/5] Do not request a pointer kaddr when not required

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Date:   Tue, 24 Jul 2018 15:41:22 +0000
From:   Huaisheng HS1 Ye <yehs1@...ovo.com>
To:     Ross Zwisler <ross.zwisler@...ux.intel.com>
CC:     "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.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>
Subject: RE: [External]  Re: [PATCH 0/5] Do not request a pointer kaddr when
 not required

From: Ross Zwisler <ross.zwisler@...ux.intel.com>
Sent: Tuesday, July 24, 2018 10:50 PM
> > Some functions within fs/dax and dax/super don't need to get kaddr from
> > direct_access. Assigning NULL to kaddr to ->direct_access() is more
> > straightforward and simple than offering a useless local pointer.
> >
> > So all direct_access() need to check the validity of second rank pointer
> > kaddr for NULL assignment. If kaddr equals to NULL, it doesn't need to
> > calculate its value.
> >
> > * This series are supplement to [PATCH v2 00/14]mm: Asynchronous +
> >   multithreaded memmap init for ZONE_DEVICE. [1]
> >
> > [1]: https://lkml.org/lkml/2018/7/16/828
> 
> This whole series looks good to me.  Just a few comments:
> 
> 1) Does this series actually depend on the "Asynchronous multithreaded mmap
> init for ZONE_DEVICE" series from Dan?  It seems totally independent to me?
> I reviewed yours by applying to linux/master, which worked fine.  I ask
> because Dan's series has been delayed to after v4.19, and if yours isn't
> actually dependent it could possibly go in sooner.

This series doesn't depend on Dan's 'Asynchronous multithreaded mmap init
for ZONE_DEVICE'. For the part as pfn, which overlaps Dan's original series.
Because I post them earlier than Dan's, Dan generously dropped the overlapping
from his series and adopted mine to the series of 'Asynchronous multithreaded'.
It is very thankful.

I knew Dan's series would be delayed, I can resend the series, both kaddr and pfn,
for faster merging to mainline.

> 2) I agree with Christian's comment that the changelogs could be improved
> slightly.  Remember that the goal of the changelog isn't to describe *what*
> the code is doing, but *why*.  We can read that the code now checks if 'kaddr'
> is NULL, and if so we don't calculate it.  It's useful to say that callers may
> have no need for 'kaddr', so this patch is prep for allowing them to pass in
> NULL instead of having to pass in a pointer that they then just throw away.

Thanks for advice. I will follow your suggestion during next submission.

> 3) I think you should make one more change to kill the unused 'dummy_addr'
> variable in persistent_memory_claim().  That was the one last case of a dummy
> 'kaddr' type variable that I could find.

Yes, you are right. I haven't updated my code base to latest mainline, so couldn't
notice it. It seems there is a new created file here as dm-writecache.c.
Thanks for hints.

Cheers,
Huaisheng Ye