On Thu, Oct 07, 2010 at 04:10:52AM +0800, Andrew Morton wrote: > On Wed, 29 Sep 2010 10:57:33 +0800 > Shaohua Li <shaohua.li@xxxxxxxxx> wrote: > > > when memory pressure is high, page_referenced() causes a lot of lock contention > > for anon_vma->lock or mapping->i_mmap_lock. Considering pages from one file > > usually live side by side in LRU list, we can lock several pages in > > shrink_page_list() and do batch page_referenced() to avoid some lock/unlock, > > which should reduce lock contention a lot. The locking rule documented in > > rmap.c is: > > page_lock > > mapping->i_mmap_lock > > anon_vma->lock > > For a batch of pages, we do page lock for all of them first and check their > > reference, and then release their i_mmap_lock or anon_vma lock. This seems not > > break the rule to me. > > Before I further polish the patch, I'd like to know if there is anything > > preventing us to do such batch here. Thanks for your time. > The patch adds quite a bit of complexity, so we'd need to see benchmark > testing results which justify it, please. My test only shows around 10% improvements, which is below my expections. try_to_unmap() causes quite a lot of lock contention for such locks, and makes the page_referenced() batch not quite helpful. Looks we can do batch try_to_unmap() too. I'll report back later when I have data with try_to_unmap() batched. Thanks, Shaohua -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>