On Thu, Feb 26, 2015 at 11:36:57AM -0800, Davidlohr Bueso wrote: > We currently use the mmap_sem to serialize the mm exe_file. > This is atrocious and a clear example of the misuses this > lock has all over the place, making any significant changes > to the address space locking that much more complex and tedious. > This also has to do of how we used to check for the vma's vm_file > being VM_EXECUTABLE (much of which was replaced by 2dd8ad81e31). > > This patch, therefore, removes the mmap_sem dependency and > introduces a specific lock for the exe_file (rwlock_t, as it is > read mostly and protects a trivial critical region). As mentioned, > the motivation is to cleanup mmap_sem (as opposed to exe_file > performance). A nice side effect of this is that we avoid taking > the mmap_sem (shared) in fork paths for the exe_file handling > (note that readers block when the rwsem is taken exclusively by > another thread). > > Now that callers have been updated and standardized[1, 2] around > the get_mm_set_exe_file() interface, changing the locking scheme > is quite straightforward. The exception being the prctl calls > (ie PR_SET_MM_EXE_FILE). Because this caller actually _updates_ > the mm->exe_file, we need to handle it in the same patch that changes > the locking rules. For this we need to reorganize prctl_set_mm_exe_file, > such that: > > o mmap_sem is taken when actually needed. > > o a new set_mm_exe_file_locked() function is introduced to be used by > prctl. We now need to explicitly acquire the exe_file_lock as before > it was implicit in holding the mmap_sem for write. > > o a new __prctl_set_mm_exe_file() helper is created, which actually > does the exe_file handling for the mm side -- needing the write > lock for updating the mm->flags (*sigh*). In the future we could > have a unique mm::exe_file_struct and keep track of MMF_EXE_FILE_CHANGED > on our own. > > mm: improve handling of mm->exe_file > [1] Part 1: https://lkml.org/lkml/2015/2/18/721 > [2] Part 2: https://lkml.org/lkml/2015/2/25/679 > > Applies on top of linux-next (20150225). > > Signed-off-by: Davidlohr Bueso <dbueso@xxxxxxx> Hi Davidlohr, it would be interesting to know if the cleanup bring some performance benefit? -- 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>