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Date:   Fri, 10 Feb 2017 08:51:11 -0800
From:   Davidlohr Bueso <>
To:     Michal Hocko <>
        Davidlohr Bueso <>
Subject: Re: [PATCH 4/4] mm,hugetlb: compute page_size_log properly

On Fri, 10 Feb 2017, Michal Hocko wrote:

>On Thu 09-02-17 12:53:02, Davidlohr Bueso wrote:
>> The SHM_HUGE_* stuff  was introduced in:
>>    42d7395feb5 (mm: support more pagesizes for MAP_HUGETLB/SHM_HUGETLB)
>> It unnecessarily adds another layer, specific to sysv shm, without
>> anything special about it: the macros are identical to the MAP_HUGE_*
>> stuff, which in turn does correctly describe the hugepage subsystem.
>> One example of the problems with extra layers what this patch fixes:
>> mmap_pgoff() should never be using SHM_HUGE_* logic. It is obviously
>> harmless but it would still be grand to get rid of it -- although
>> now in the manpages I don't see that happening.
>Can we just drop SHM_HUGE_MASK altogether? It is not exported in uapi
>headers AFAICS.

Yeah that was my original idea, however I noticed that shmget.2 mentions
kernel internals as part of SHM_HUGE_{2MB,1GB}, ie: SHM_HUGE_SHIFT. So
dropping _MASK doesn't make sense if we are going to keep _SHIFT.


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