linux-kernel - Re: [PATCH 4/4] mm,hugetlb: compute page_size

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Date:   Fri, 10 Feb 2017 11:20:44 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Davidlohr Bueso <dave@...olabs.net>
Cc:     akpm@...ux-foundation.org, manfred@...orfullife.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Davidlohr Bueso <dbueso@...e.de>
Subject: Re: [PATCH 4/4] mm,hugetlb: compute page_size_log properly

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.

> 
> Cc: linux-mm@...ck.org
> Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
> ---
>  mm/mmap.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 499b988b1639..40b29aca18c1 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1479,7 +1479,7 @@ SYSCALL_DEFINE6(mmap_pgoff, unsigned long, addr, unsigned long, len,
>  		struct user_struct *user = NULL;
>  		struct hstate *hs;
>  
> -		hs = hstate_sizelog((flags >> MAP_HUGE_SHIFT) & SHM_HUGE_MASK);
> +		hs = hstate_sizelog((flags >> MAP_HUGE_SHIFT) & MAP_HUGE_MASK);
>  		if (!hs)
>  			return -EINVAL;
>  
> -- 
> 2.6.6
> 
> --
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-- 
Michal Hocko
SUSE Labs