Messages in this thread | | | Subject | Re: [PATCH 2/3] Reserve huge pages for reliable MAP_PRIVATE hugetlbfs mappings until fork() | From | Adam Litke <> | Date | Wed, 28 May 2008 08:52:44 -0500 |
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On Tue, 2008-05-27 at 19:51 +0100, Mel Gorman wrote: > This patch reserves huge pages at mmap() time for MAP_PRIVATE mappings in a > similar manner to the reservations taken for MAP_SHARED mappings. The reserve count is > accounted both globally and on a per-VMA basis for private mappings. This > guarantees that a process that successfully calls mmap() will successfully > fault all pages in the future unless fork() is called. > > The characteristics of private mappings of hugetlbfs files behaviour after > this patch are; > > 1. The process calling mmap() is guaranteed to succeed all future faults until > it forks(). > 2. On fork(), the parent may die due to SIGKILL on writes to the private > mapping if enough pages are not available for the COW. For reasonably > reliable behaviour in the face of a small huge page pool, children of > hugepage-aware processes should not reference the mappings; such as > might occur when fork()ing to exec(). > 3. On fork(), the child VMAs inherit no reserves. Reads on pages already > faulted by the parent will succeed. Successful writes will depend on enough > huge pages being free in the pool. > 4. Quotas of the hugetlbfs mount are checked at reserve time for the mapper > and at fault time otherwise. > > Before this patch, all reads or writes in the child potentially needs page > allocations that can later lead to the death of the parent. This applies > to reads and writes of uninstantiated pages as well as COW. After the > patch it is only a write to an instantiated page that causes problems. > > Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Acked-by: Adam Litke <agl@us.ibm.com>
-- Adam Litke - (agl at us.ibm.com) IBM Linux Technology Center
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