On Wed 10-07-19 16:36:58, Mike Kravetz wrote: > On 7/10/19 12:44 PM, Michal Hocko wrote: > > On Wed 10-07-19 11:42:40, Mike Kravetz wrote: > > [...] > >> As Michal suggested, I'm going to do some testing to see what impact > >> dropping the __GFP_RETRY_MAYFAIL flag for these huge page allocations > >> will have on the number of pages allocated. > > > > Just to clarify. I didn't mean to drop __GFP_RETRY_MAYFAIL from the > > allocation request. I meant to drop the special casing of the flag in > > should_continue_reclaim. I really have hard time to argue for this > > special casing TBH. The flag is meant to retry harder but that shouldn't > > be reduced to a single reclaim attempt because that alone doesn't really > > help much with the high order allocation. It is more about compaction to > > be retried harder. > > Thanks Michal. That is indeed what you suggested earlier. I remembered > incorrectly. Sorry. > > Removing the special casing for __GFP_RETRY_MAYFAIL in should_continue_reclaim > implies that it will return false if nothing was reclaimed (nr_reclaimed == 0) > in the previous pass. > > When I make such a modification and test, I see long stalls as a result > of should_compact_retry returning true too often. On a system I am currently > testing, should_compact_retry has returned true 36000000 times. My guess > is that this may stall forever. Vlastmil previously asked about this behavior, > so I am capturing the reason. Like before [1], should_compact_retry is > returning true mostly because compaction_withdrawn() returns COMPACT_DEFERRED. This smells like a problem to me. But somebody more familiar with compaction should comment. > > Total 36000000 > 35437500 COMPACT_DEFERRED > 562500 COMPACT_PARTIAL_SKIPPED > > > [1] https://lkml.org/lkml/2019/6/5/643 > -- > Mike Kravetz -- Michal Hocko SUSE Labs
