> On Thu, Sep 09, 2010 at 01:13:22PM +0900, KOSAKI Motohiro wrote: > > > On Thu, 9 Sep 2010 12:04:48 +0900 > > > KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: > > > > > > > On Mon, 6 Sep 2010 11:47:28 +0100 > > > > Mel Gorman <mel@xxxxxxxxx> wrote: > > > > > > > > > From: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> > > > > > > > > > > With synchrounous lumpy reclaim, there is no reason to give up to reclaim > > > > > pages even if page is locked. This patch uses lock_page() instead of > > > > > trylock_page() in this case. > > > > > > > > > > Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> > > > > > Signed-off-by: Mel Gorman <mel@xxxxxxxxx> > > > > > > > > Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> > > > > > > > Ah......but can't this change cause dead lock ?? > > > > Yes, this patch is purely crappy. please drop. I guess I was poisoned > > by poisonous mushroom of Mario Bros. > > > > Lets be clear on what the exact dead lock conditions are. The ones I had > thought about when I felt this patch was ok were; > > o We are not holding the LRU lock (or any lock, we just called cond_resched()) > o We do not have another page locked because we cannot lock multiple pages > o Kswapd will never be in LUMPY_MODE_SYNC so it is not getting blocked > o lock_page() itself is not allocating anything that we could recurse on True, all. > > One potential dead lock would be if the direct reclaimer held a page > lock and ended up here but is that situation even allowed? example, __do_fault() { (snip) if (unlikely(!(ret & VM_FAULT_LOCKED))) lock_page(vmf.page); else VM_BUG_ON(!PageLocked(vmf.page)); /* * Should we do an early C-O-W break? */ page = vmf.page; if (flags & FAULT_FLAG_WRITE) { if (!(vma->vm_flags & VM_SHARED)) { anon = 1; if (unlikely(anon_vma_prepare(vma))) { ret = VM_FAULT_OOM; goto out; } page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address); Afaik, detailed rule is, o kswapd can call lock_page() because they never take page lock outside vmscan o if try_lock() is successed, we can call lock_page_nosync() against its page after unlock. because the task have gurantee of no lock taken. o otherwise, direct reclaimer can't call lock_page(). the task may have a lock already. I think. > I did not > think of an obvious example of when this would happen. Similarly, > deadlock situations with mmap_sem shouldn't happen unless multiple page > locks are being taken. > > (prepares to feel foolish) > > What did I miss? -- 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>