On 2/2/22 17:53, Waiman Long wrote: > > On 2/1/22 10:28, Michal Hocko wrote: >> Cc Vlastimil >> >> On Mon 31-01-22 17:03:28, Waiman Long wrote: >>> The page_owner information currently includes the pid of the calling >>> task. That is useful as long as the task is still running. Otherwise, >>> the number is meaningless. To have more information about the allocating >>> tasks that had exited by the time the page_owner information is >>> retrieved, we need to store the command name of the task. >>> >>> Add a new comm field into page_owner structure to store the command name >>> and display it when the page_owner information is retrieved. >> I completely agree that pid is effectivelly useless (if not misleading) >> but is comm really telling all that much to compensate for the >> additional storage required for _each_ page in the system? > > Yes, it does add an extra 16 bytes per page overhead. The command name can > be useful if one want to find out which userspace command is responsible for > a problematic page allocation. Maybe we can remove pid from page_owner to > save 8 bytes as you also agree that this number is not that useful. Pid could be used to correlate command instances (not perfectly if reuse happens), but command name could have a higher chance to be useful. In my experience the most useful were the stacktraces and gfp/order etc. anyway. So I wouldn't be opposed replacing pid with comm. The mild size increase should be acceptable, this is an opt-in feature for debugging sessions with known tradeoff for memory and cpu overhead for the extra info. > Cheers, > Longman >
