Messages in this thread | | | Date | Sat, 03 Feb 2007 07:35:59 -0800 | From | "Martin J. Bligh" <> | Subject | Re: [RFC] Tracking mlocked pages and moving them off the LRU |
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Christoph Hellwig wrote: > On Fri, Feb 02, 2007 at 10:20:12PM -0800, Christoph Lameter wrote: >> This is a new variation on the earlier RFC for tracking mlocked pages. >> We now mark a mlocked page with a bit in the page flags and remove >> them from the LRU. Pages get moved back when no vma that references >> the page has VM_LOCKED set anymore. >> >> This means that vmscan no longer uselessly cycles over large amounts >> of mlocked memory should someone attempt to mlock large amounts of >> memory (may even result in a livelock on large systems). >> >> Synchronization is build around state changes of the PageMlocked bit. >> The NR_MLOCK counter is incremented and decremented based on >> state transitions of PageMlocked. So the count is accurate. >> >> There is still some unfinished business: >> >> 1. We use the 21st page flag and we only have 20 on 32 bit NUMA platforms. >> >> 2. Since mlocked pages are now off the LRU page migration will no longer >> move them. >> >> 3. Use NR_MLOCK to tune various VM behaviors so that the VM does not >> longer fall due to too many mlocked pages in certain areas. > > This patch seems to not handle the cases where more than one process mlocks > a page and you really need a pincount in the page to not release it before > all processes have munlock it or died. I did a similar patch a while > ago and tried to handle it by overloading the lru lists pointers with > a pincount, but at some point I gave up because I couldn't get that part > right.
Doesn't matter - you can just do it lazily. If you find a page that is locked, move it to the locked list. when unlocking a page you *always* move it back to the normal list. If someone else is still locking it, we'll move it back to the lock list on next reclaim pass.
I have a half-finished patch from 6 months ago that does this, but never found time to complete it ;-(
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