linux-kernel - Re: [PATCH 3/6] pmem: pmem_dax_direct_access() to honor the DAXDEV_F

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Date:   Thu, 21 Oct 2021 18:24:03 +0000
From:   Jane Chu <jane.chu@...cle.com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     "david@...morbit.com" <david@...morbit.com>,
        "djwong@...nel.org" <djwong@...nel.org>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "vishal.l.verma@...el.com" <vishal.l.verma@...el.com>,
        "dave.jiang@...el.com" <dave.jiang@...el.com>,
        "agk@...hat.com" <agk@...hat.com>,
        "snitzer@...hat.com" <snitzer@...hat.com>,
        "dm-devel@...hat.com" <dm-devel@...hat.com>,
        "ira.weiny@...el.com" <ira.weiny@...el.com>,
        "willy@...radead.org" <willy@...radead.org>,
        "vgoyal@...hat.com" <vgoyal@...hat.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "nvdimm@...ts.linux.dev" <nvdimm@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>
Subject: Re: [PATCH 3/6] pmem: pmem_dax_direct_access() to honor the
 DAXDEV_F_RECOVERY flag

On 10/21/2021 4:23 AM, Christoph Hellwig wrote:
> On Wed, Oct 20, 2021 at 06:10:56PM -0600, Jane Chu wrote:
>> -	if (unlikely(is_bad_pmem(&pmem->bb, PFN_PHYS(pgoff) / 512,
>> -					PFN_PHYS(nr_pages))))
>> +	if (unlikely(!(flags & DAXDEV_F_RECOVERY) &&
>> +		is_bad_pmem(&pmem->bb, PFN_PHYS(pgoff) / 512,
>> +				PFN_PHYS(nr_pages))))
> 
> The indentation here is pretty messed up. Something like this would
> be move normal:
> 
> 	if (unlikely(!(flags & DAXDEV_F_RECOVERY) &&
> 			is_bad_pmem(&pmem->bb, PFN_PHYS(pgoff) / 512,
> 				    PFN_PHYS(nr_pages)))) {
> 

Will do.

> but if we don't really need the unlikely we could do an actually
> readable variant:
> 
> 	if (!(flags & DAXDEV_F_RECOVERY) &&
> 	    is_bad_pmem(&pmem->bb, PFN_PHYS(pgoff) / 512, PFN_PHYS(nr_pages)))
> 

'unlikely' is needed because 'RWF_RECOVERY_DATA' flag is not
recommended for normal preadv2/pwritev2 usage, it's recommended
only if user is aware of or suspect poison in the range.

thanks,
-jane