Re: [PATCH 07/12] mm, thp, tmpfs: handle huge page inshmem_undo_range for truncate

[Ning Qu]

Best wishes,
-- 
Ning Qu (æå) | Software Engineer | quning@xxxxxxxxxx | +1-408-418-6066


On Wed, Oct 16, 2013 at 5:09 AM, Kirill A. Shutemov
<kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
> Ning Qu wrote:
>> > Again. Here and below ifdef is redundant: PageTransHugeCache() is zero
>> > compile-time and  thp case will be optimize out.
>>
>> The problem is actually from HPAGE_CACHE_INDEX_MASK, it is marked as
>> build bug when CONFIG_TRANSPARENT_HUGEPAGE_PAGECACHE is false. So we
>> either wrap some logic inside a inline function, or we have to be like
>> this .. Or we don't treat the HPAGE_CACHE_INDEX_MASK as a build bug?
>
> HPAGE_CACHE_INDEX_MASK shouldn't be a problem.
> If it's wrapped into 'if PageTransHugeCache(page)' or similar it will be
> eliminated by compiler if thp-pc disabled and build bug will not be
> triggered.
>
>>
>> >
>> > And do we really need a copy of truncate logic here? Is there a way to
>> > share code?
>> >
>> The truncate between tmpfs and general one is similar but not exactly
>> the same (no readahead), so share the whole function might not be a
>> good choice from the perspective of tmpfs? Anyway, there are other
>> similar functions in tmpfs, e.g. the one you mentioned for
>> shmem_add_to_page_cache. It is possible to share the code, I am just
>> worried it will make the logic more complicated?
>
> I think introducing thp-pc is good opportunity to refactor all these code.

I agree, I review the code of generate truncate and shmem_undo_range again.
There are just too many differences in almost every major piece of
logic. It's really
not possible to extract any meaningful common function to share between them.

And I agree, we will try to refactor any other functions which are
possible. Thanks!

>
> --
>  Kirill A. Shutemov
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