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

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Message-ID: <057b01d06dde$71738db0$545aa910$@alibaba-inc.com>
Date:	Fri, 03 Apr 2015 15:18:50 +0800
From:	"Hillf Danton" <hillf.zj@...baba-inc.com>
To:	"David Rientjes" <rientjes@...gle.com>
Cc:	<linux-mm@...ck.org>,
	"linux-kernel" <linux-kernel@...r.kernel.org>,
	"Andrew Morton" <akpm@...ux-foundation.org>
Subject: Re: [patch -mm] mm, doc: cleanup and clarify munmap behavior for hugetlb memory fix

> 
> 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>
> ---
Acked-by: Hillf Danton <hillf.zj@...baba-inc.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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