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. That said, some optimisations are still included but much reduced. For example, list rotations are still there but it's very straight-forward. 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'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. -- Mel Gorman SUSE Labs
