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[PATCH 4/4] mm,hugetlb: compute page_size_log properly

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  [PATCH 4/4] mm,hugetlb: compute page_size_log properly Davidlohr Bueso <dave@stgolabs.net> - 2017-02-09 22:00 +0100
    Re: [PATCH 4/4] mm,hugetlb: compute page_size_log properly Michal Hocko <mhocko@kernel.org> - 2017-02-10 11:30 +0100
      Re: [PATCH 4/4] mm,hugetlb: compute page_size_log properly Davidlohr Bueso <dave@stgolabs.net> - 2017-02-10 18:00 +0100

#1577948 — [PATCH 4/4] mm,hugetlb: compute page_size_log properly

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.

Cc: linux-mm@kvack.org
Signed-off-by: Davidlohr Bueso <dbueso@suse.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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#1578366

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@kvack.org
> Signed-off-by: Davidlohr Bueso <dbueso@suse.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
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

-- 
Michal Hocko
SUSE Labs

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#1578622

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.

Thanks,
Davidlohr

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