On Mon 07-10-13 15:38:24, Marciniszyn, Mike wrote: > > > This patch and the sibling ipath patch will nominally take the mmap_sem > > > twice where the old routine only took it once. This is a performance > > > issue. > > It will take mmap_sem only once during normal operation. Only if > > get_user_pages_unlocked() fail, we have to take mmap_sem again to undo > > the change of mm->pinned_vm. > > > > > Is the intent here to deprecate get_user_pages()? > > The old code looked like: > __qib_get_user_pages() > (broken) ulimit test > for (...) > get_user_pages() > > qib_get_user_pages() > mmap_sem lock > __qib_get_user_pages() > mmap_sem() unlock > > The new code is: > > get_user_pages_unlocked() > mmap_sem lock > get_user_pages() > mmap_sem unlock > > qib_get_user_pages() > mmap_sem lock > ulimit test and locked pages maintenance > mmap_sem unlock > for (...) > get_user_pages_unlocked() > > I count an additional pair of mmap_sem transactions in the normal case. Ah, sorry, you are right. > > > Could the lock limit test be pushed into another version of the > > > wrapper so that there is only one set of mmap_sem transactions? > > I'm sorry, I don't understand what you mean here... > > > > This is what I had in mind: > > get_user_pages_ulimit_unlocked() > mmap_sem lock > ulimit test and locked pages maintenance (from qib/ipath) > for (...) > get_user_pages_unlocked() > mmap_sem unlock > > qib_get_user_pages() > get_user_pages_ulimit_unlocked() > > This really pushes the code into a new wrapper common to ipath/qib and > any others that might want to combine locking with ulimit enforcement. We could do that but frankly, I'd rather change ulimit enforcement to not require mmap_sem and use atomic counter instead. I'll see what I can do. Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- 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>