On Tue, Jul 25, 2017 at 12:47:41AM -0400, Prakash Sangappa wrote: > In some cases, userfaultfd mechanism should just deliver a SIGBUS signal > to the faulting process, instead of the page-fault event. Dealing with > page-fault event using a monitor thread can be an overhead in these > cases. For example applications like the database could use the signaling > mechanism for robustness purpose. > > Database uses hugetlbfs for performance reason. Files on hugetlbfs > filesystem are created and huge pages allocated using fallocate() API. > Pages are deallocated/freed using fallocate() hole punching support. > These files are mmapped and accessed by many processes as shared memory. > The database keeps track of which offsets in the hugetlbfs file have > pages allocated. > > Any access to mapped address over holes in the file, which can occur due > to bugs in the application, is considered invalid and expect the process > to simply receive a SIGBUS. However, currently when a hole in the file is > accessed via the mapped address, kernel/mm attempts to automatically > allocate a page at page fault time, resulting in implicitly filling the > hole in the file. This may not be the desired behavior for applications > like the database that want to explicitly manage page allocations of > hugetlbfs files. > > Using userfaultfd mechanism with this support to get a signal, database > application can prevent pages from being allocated implicitly when > processes access mapped address over holes in the file. > > This patch adds UFFD_FEATURE_SIGBUS feature to userfaultfd mechnism to > request for a SIGBUS signal. > > See following for previous discussion about the database requirement > leading to this proposal as suggested by Andrea. > > http://www.spinics.net/lists/linux-mm/msg129224.html > > Signed-off-by: Prakash Sangappa <prakash.sangappa@xxxxxxxxxx> > --- > fs/userfaultfd.c | 3 +++ > include/uapi/linux/userfaultfd.h | 10 +++++++++- > 2 files changed, 12 insertions(+), 1 deletions(-) Reviewed-by: Andrea Arcangeli <aarcange@xxxxxxxxxx> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
