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

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

[Hillf Danton]

> 
> 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@google.com>
> ---
Acked-by: Hillf Danton <hillf.zj@alibaba-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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Re: [patch -mm] mm, doc: cleanup and clarify munmap behavior for hugetlb memory fix

[Jonathan Corbet]

On Thu, 9 Apr 2015 12:46:09 -0700 (PDT)
David Rientjes <rientjes@google.com> wrote:

> It's been merged into that tree, but I would still appreciate your 
> ack!

Easy enough.

Acked-by: Jonathan Corbet <corbet@lwn.net>

jon

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

[David Rientjes]

On Sat, 4 Apr 2015, Jonathan Corbet wrote:

> On Thu, 2 Apr 2015 15:50:15 -0700 (PDT)
> David Rientjes <rientjes@google.com> 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.
> 
> So I was going to apply this to the docs tree, but it doesn't even come
> close.  What tree was this patch generated against?
> 

Sorry, it's not intended to go through the docs tree, it's a patch to fix 
mm-doc-cleanup-and-clarify-munmap-behavior-for-hugetlb-memory.patch in 
-mm.  It's been merged into that tree, but I would still appreciate your 
ack!

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

[Jonathan Corbet]

On Thu, 2 Apr 2015 15:50:15 -0700 (PDT)
David Rientjes <rientjes@google.com> 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.

So I was going to apply this to the docs tree, but it doesn't even come
close.  What tree was this patch generated against?

Thanks,

jon

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

[Hugh Dickins]

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@google.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@google.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

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

[David Rientjes]

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@google.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