On Wed, Jul 17, 2013 at 12:50:25PM -0700, Davidlohr Bueso wrote: > From: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx> > > At present, the page fault path for hugepages is serialized by a > single mutex. This is used to avoid spurious out-of-memory conditions > when the hugepage pool is fully utilized (two processes or threads can > race to instantiate the same mapping with the last hugepage from the > pool, the race loser returning VM_FAULT_OOM). This problem is > specific to hugepages, because it is normal to want to use every > single hugepage in the system - with normal pages we simply assume > there will always be a few spare pages which can be used temporarily > until the race is resolved. > > Unfortunately this serialization also means that clearing of hugepages > cannot be parallelized across multiple CPUs, which can lead to very > long process startup times when using large numbers of hugepages. > > This patch improves the situation by replacing the single mutex with a > table of mutexes, selected based on a hash, which allows us to know > which page in the file we're instantiating. For shared mappings, the > hash key is selected based on the address space and file offset being faulted. > Similarly, for private mappings, the mm and virtual address are used. > Hello. With this table mutex, we cannot protect region tracking structure. See below comment. /* * Region tracking -- allows tracking of reservations and instantiated pages * across the pages in a mapping. * * The region data structures are protected by a combination of the mmap_sem * and the hugetlb_instantion_mutex. To access or modify a region the caller * must either hold the mmap_sem for write, or the mmap_sem for read and * the hugetlb_instantiation mutex: * * down_write(&mm->mmap_sem); * or * down_read(&mm->mmap_sem); * mutex_lock(&hugetlb_instantiation_mutex); */ Thanks. -- 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>