Re: [patch -mm] mm, doc: cleanup and clarify munmap behavior for hugetlb memory fix
From: Hugh Dickins <hughd@google.com>
Date: 2015-04-03 01:05:22
Also in:
linux-mm, lkml
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>
quoted hunk ↗ jump to hunk
--- 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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