Messages in this thread | | | Subject | Re: [RFC][PATCH] lru_add_drain_all() don't use schedule_on_each_cpu() | From | Lee Schermerhorn <> | Date | Tue, 28 Oct 2008 17:29:26 -0400 |
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On Tue, 2008-10-28 at 13:45 -0700, Andrew Morton wrote: > On Tue, 28 Oct 2008 09:25:31 -0500 (CDT) > Christoph Lameter <cl@linux-foundation.org> wrote: > > > On Mon, 27 Oct 2008, Andrew Morton wrote: > > > > > Can we fix that instead? > > > > How about this fix? > > > > > > > > Subject: Move migrate_prep out from under mmap_sem > > > > Move the migrate_prep outside the mmap_sem for the following system calls > > > > 1. sys_move_pages > > 2. sys_migrate_pages > > 3. sys_mbind() > > > > It really does not matter when we flush the lru. The system is free to add > > pages onto the lru even during migration which will make the page > > migration either skip the page (mbind, migrate_pages) or return a busy > > state (move_pages). > > > > That looks nicer, thanks. Hopefully it fixes the > lockdep-warning/deadlock...
I believe that we still have the lru_drain_all() called from the fault path [with mmap_sem held] in clear_page_mlock(). We call clear_page_mlock() on COW of an mlocked page in a VM_LOCKED vma to ensure that we don't end up with an mlocked page in some other task's non-VM_LOCKED vma where we'd then fail to munlock it later. During development testing, Rik encountered scenarios where a page would encounter a COW fault while it was still making its way to the LRU via the pagevecs. So, he added the 'drain_all() and that seemed to avoid this scenario.
Now, in the current upstream version of the unevictable mlocked pages patches, we just count any mlocked pages [vmstat] that make their way to free*page() instead of BUGging out, as we were doing earlier during development. So, maybe we can drop the lru_drain_add()s in the unevictable mlocked pages work and live with the occasional freed mlocked page, or mlocked page on the active/inactive lists to be dealt with by vmscan.
Comments?
Lee
> > I guess we should document our newly discovered schedule_on_each_cpu() > problems before we forget about it and later rediscover it.
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