Re: [PATCH] filemap : fix the wrong offset

[Huang Shijie <shijie8@gmail.com>]

Hugh Dickins wrote:
> I really think this issue is better ignored.  There was a time,
> seven years ago, when I cared about it, and made such corrections
> in mm/shmem.c.  But we're chipping away at the tip of the iceberg
> here, and it's just a waste of everybody's time for so long as
> PAGE_CACHE_SIZE == PAGE_SIZE.
>
> There have been patches experimenting with PAGE_CACHE_SIZE multiple
> of PAGE_SIZE (and probably not PAGE_SIZE multiple of PAGE_CACHE_SIZE);
> and I've come to the conclusion that the only sensible place for these
> PAGE_CACHE_SHIFT - PAGE_SHIFT patches is in a patch which really makes
> that difference.
>
> I wish PAGE_CACHE_SIZE had never been added in the first place,
> long before it was needed; but ripping it out doesn't seem quite
> the right thing to do either; and likewise I leave a smattering of
> PAGE_CACHE_SHIFT - PAGE_SHIFT lines in, just to remind us from time
> to time that there might one day be a difference.
>
>   
Ok. I get it.

But the filemap_fault()  looks  strange. Some functions such as 
do_sync_mmap_readahead() treat offset
in the PAGE_CAHE_SHIFT unit,though offset is actually in the PAGE_SHIFT 
unit.
> I know this is a very unsatisfying response: but you and I
> and everyone else have better things to spend our time on.
> Thinking about the difference between two things that are
> always the same is rather a waste of mental energy.
>   
Thanks a lot for your explanation.

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