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Subject: Re: [RFC] nvfs: a filesystem for persistent memory
To: Matthew Wilcox <willy@infradead.org>,
        Mikulas Patocka <mpatocka@redhat.com>
References: <alpine.LRH.2.02.2009140852030.22422@file01.intranet.prod.int.rdu2.redhat.com>
 <20200915130012.GC5449@casper.infradead.org>
From: Ritesh Harjani <riteshh@linux.ibm.com>
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Date: Tue, 22 Sep 2020 15:34:37 +0530
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On 9/15/20 6:30 PM, Matthew Wilcox wrote:
> On Tue, Sep 15, 2020 at 08:34:41AM -0400, Mikulas Patocka wrote:
>> - when the fsck.nvfs tool mmaps the device /dev/pmem0, the kernel uses
>> buffer cache for the mapping. The buffer cache slows does fsck by a factor
>> of 5 to 10. Could it be possible to change the kernel so that it maps DAX
>> based block devices directly?
> 
> Oh, because fs/block_dev.c has:
>          .mmap           = generic_file_mmap,
> 
> I don't see why we shouldn't have a blkdev_mmap modelled after
> ext2_file_mmap() with the corresponding blkdev_dax_vm_ops.
> 

pls help with below 2 queries:-

1. Can't we use ->direct_IO here to avoid the mentioned performance problem?
2. Any other existing use case where having this blkdev_dax_vm_ops be 
useful?

-ritesh
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