On 04/10/2013 02:23 PM, Andrew Morton wrote:
On Wed, 10 Apr 2013 11:23:28 -0700 Cody P Schafer <cody@xxxxxxxxxxxxxxxxxx> wrote:"Problems" with the current code: 1. there is a lack of synchronization in setting ->high and ->batch in percpu_pagelist_fraction_sysctl_handler() 2. stop_machine() in zone_pcp_update() is unnecissary. 3. zone_pcp_update() does not consider the case where percpu_pagelist_fraction is non-zero To fix: 1. add memory barriers, a safe ->batch value, an update side mutex when updating ->high and ->batch, and use ACCESS_ONCE() for ->batch users that expect a stable value. 2. avoid draining pages in zone_pcp_update(), rely upon the memory barriers added to fix #1 3. factor out quite a few functions, and then call the appropriate one. Note that it results in a change to the behavior of zone_pcp_update(), which is used by memory_hotplug. I'm rather certain that I've diserned (and preserved) the essential behavior (changing ->high and ->batch), and only eliminated unneeded actions (draining the per cpu pages), but this may not be the case. Further note that the draining of pages that previously took place in zone_pcp_update() occured after repeated draining when attempting to offline a page, and after the offline has "succeeded". It appears that the draining was added to zone_pcp_update() to avoid refactoring setup_pageset() into 2 funtions.There hasn't been a ton of review activity for this patchset :( I'm inclined to duck it until after 3.9. Do the patches fix any noticeably bad userspace behavior?
No, all the bugs are theoretical. Waiting should be fine. -- 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>