On Fri, 2019-12-13 at 11:08 +0000, Mel Gorman wrote: > On Fri, Dec 13, 2019 at 11:00:42AM +0100, David Hildenbrand wrote: > > > A brief history on the background of free page reporting can be found at: > > > https://lore.kernel.org/lkml/29f43d5796feed0dec8e8bb98b187d9dac03b900.camel@xxxxxxxxxxxxxxx/ > > > > > > Changes from v13: > > > https://lore.kernel.org/lkml/20191105215940.15144.65968.stgit@localhost.localdomain/ > > > Rewrote core reporting functionality > > > Merged patches 3 & 4 > > > Dropped boundary list and related code > > > Folded get_reported_page into page_reporting_fill > > > Folded page_reporting_fill into page_reporting_cycle > > > Pulled reporting functionality out of free_reported_page > > > Renamed it to __free_isolated_page > > > Moved page reporting specific bits to page_reporting_drain > > > Renamed phdev to prdev since we aren't "hinting" we are "reporting" > > > Added documentation to describe the usage of unused page reporting > > > Updated cover page and patch descriptions to avoid mention of boundary > > > > > > Changes from v14: > > > https://lore.kernel.org/lkml/20191119214454.24996.66289.stgit@localhost.localdomain/ > > > Renamed "unused page reporting" to "free page reporting" > > > Updated code, kconfig, and patch descriptions > > > Split out patch for __free_isolated_page > > > Renamed function to __putback_isolated_page > > > Rewrote core reporting functionality > > > Added logic to reschedule worker in 2 seconds instead of run to completion > > > Removed reported_pages statistics > > > Removed REPORTING_REQUESTED bit used in zone flags > > > Replaced page_reporting_dev_info refcount with state variable > > > Removed scatterlist from page_reporting_dev_info > > > Removed capacity from page reporting device > > > Added dynamic scatterlist allocation/free at start/end of reporting process > > > Updated __free_one_page so that reported pages are not always added to tail > > > Added logic to handle error from report function > > > Updated virtio-balloon patch that adds support for page reporting > > > Updated patch description to try and highlight differences in approaches > > > Updated logic to reflect that we cannot limit the scatterlist from device > > > > Last time Mel said > > > > "Ok, I'm ok with how this hooks into the allocator as the overhead is > > minimal. However, the patch itself still includes a number of > > optimisations instead of being a bare-boned implementation of the > > feature with optimisations layered on top." > > > > I didn't get the chance to take a close look as I'm trying to clear as > much as possible from my table on the run-up to Christmas so I don't come > back to a disaster inbox. I also noted that the Acks for earlier patches > were not included so I was uncertain if doing a full review would still > be a good use of time when time was tight. Sorry about that. I will go back through and make sure to collect the Acks on the earlier patches. I guess I had overlooked them while focusing on rewriting the core functionality. > That said, some optimisations are still included but much reduced. For > example, list rotations are still there but it's very straight-forward. I will go ahead and split the rotations out into a separate patch for v16. I can probably do that and pull the budget bit I had added out and put it together as a "work conserving/limiting" optimization for the patch set. > The refcount is gone which is good and replaced by a state, which could be > be better documented, but is more straight forward and the zone->lock is > back protecting the free lists primarily and not zone metadata or prdev > metadata (at least not obviously). I didn't put in the time to see if > the atomic_set in page_reporting_process() is ok or whether state could > be lost but I *think* it's ok because it should be called from just one > workqueue request and they shouldn't be stacked. A comment there explaining > why atomic_set is definitely correct would be helpful. I will go though and add some more documentation about the state. > I'm inclined to decide that yes, this version is potentially ok as a > bare minimum but didn't put in the time to be 100% sure. Sounds good. I will go through and address the concerns you brought up, and probably post a v16 by the end of next week. Thanks for the feedback. - Alex
