linux-kernel - Re: [patch -mm] mm, doc: cleanup and clarify munmap behavior for hugetlb memory fix

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Message-ID: <alpine.LSU.2.11.1504021802340.7876@eggly.anvils>
Date:	Thu, 2 Apr 2015 18:05:10 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	David Rientjes <rientjes@...gle.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	Jonathan Corbet <corbet@....net>,
	Davide Libenzi <davidel@...ilserver.org>,
	Luiz Capitulino <lcapitulino@...hat.com>,
	Shuah Khan <shuahkh@....samsung.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Joern Engel <joern@...fs.org>,
	Jianguo Wu <wujianguo@...wei.com>,
	Eric B Munson <emunson@...mai.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	linux-doc@...r.kernel.org
Subject: Re: [patch -mm] mm, doc: cleanup and clarify munmap behavior for
 hugetlb memory fix

On Thu, 2 Apr 2015, David Rientjes wrote:

> Don't only specify munmap(2) behavior with respect the hugetlb memory, all 
> other syscalls get naturally aligned to the native page size of the 
> processor.  Rather, pick out munmap(2) as a specific example.
> 
> Signed-off-by: David Rientjes <rientjes@...gle.com>

Thanks, yes, good wording: it is best to be a bit vague here,
since each msyscall takes the approach most convenient for it.

Acked-by: Hugh Dickins <hughd@...gle.com>

> ---
>  Documentation/vm/hugetlbpage.txt | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/vm/hugetlbpage.txt b/Documentation/vm/hugetlbpage.txt
> index 1270fb1..030977f 100644
> --- a/Documentation/vm/hugetlbpage.txt
> +++ b/Documentation/vm/hugetlbpage.txt
> @@ -313,8 +313,11 @@ into /proc/sys/vm/hugetlb_shm_group.  It is possible for same or different
>  applications to use any combination of mmaps and shm* calls, though the mount of
>  filesystem will be required for using mmap calls without MAP_HUGETLB.
>  
> -When using munmap(2) to unmap hugetlb memory, the length specified must be
> -hugepage aligned, otherwise it will fail with errno set to EINVAL.
> +Syscalls that operate on memory backed by hugetlb pages only have their lengths
> +aligned to the native page size of the processor; they will normally fail with
> +errno set to EINVAL or exclude hugetlb pages that extend beyond the length if
> +not hugepage aligned.  For example, munmap(2) will fail if memory is backed by
> +a hugetlb page and the length is smaller than the hugepage size.
>  
>  
>  Examples
--
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