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Subject: Re: [PATCH v7 01/24] mm: Move readahead prototypes from mm.h
To: Matthew Wilcox <willy@infradead.org>
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From: John Hubbard <jhubbard@nvidia.com>
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On 2/21/20 1:48 PM, Matthew Wilcox wrote:
> On Thu, Feb 20, 2020 at 06:43:31PM -0800, John Hubbard wrote:
>> Yes. But I think these files also need a similar change:
>>
>>     fs/btrfs/disk-io.c
> 
> That gets pagemap.h through ctree.h, so I think it's fine.  It's
> already using mapping_set_gfp_mask(), so it already depends on pagemap.h.
> 
>>     fs/nfs/super.c
> 
> That gets it through linux/nfs_fs.h.
> 
> I was reluctant to not add it to blk-core.c because it doesn't seem
> necessarily intuitive that the block device core would include pagemap.h.
> 
> That said, blkdev.h does include pagemap.h, so maybe I don't need to
> include it here.

OK. Looks good (either through blkdev.h or as-is), so:

    Reviewed-by: John Hubbard <jhubbard@nvidia.com>


> 
>> ...because they also use VM_READAHEAD_PAGES, and do not directly include
>> pagemap.h yet.
> 
>>> +#define VM_READAHEAD_PAGES	(SZ_128K / PAGE_SIZE)
>>> +
>>> +void page_cache_sync_readahead(struct address_space *, struct file_ra_state *,
>>> +		struct file *, pgoff_t index, unsigned long req_count);
>>
>> Yes, "struct address_space *mapping" is weird, but I don't know if it's
>> "misleading", given that it's actually one of the things you have to learn
>> right from the beginning, with linux-mm, right? Or is that about to change?
>>
>> I'm not asking to restore this to "struct address_space *mapping", but I thought
>> it's worth mentioning out loud, especially if you or others are planning on
>> changing those names or something. Just curious.
> 
> No plans (on my part) to change the name, although I have heard people
> grumbling that there's very little need for it to be a separate struct
> from inode, except for the benefit of coda, which is not exactly a
> filesystem with a lot of users ...
> 
> Anyway, no plans to change it.  If there were something _special_ about
> it like a theoretical:
> 
> void mapping_dedup(struct address_space *canonical,
> 		struct address_space *victim);
> 
> then that's useful information and shouldn't be deleted.  But I don't
> think the word 'mapping' there conveys anything useful (other than the
> convention is to call a 'struct address_space' a mapping, which you'll
> see soon enough once you look at any of the .c files).
> 

OK, that's consistent and makes sense.


thanks,
-- 
John Hubbard
NVIDIA