On Tue 31-10-17 21:42:23, Tetsuo Handa wrote: > Michal Hocko wrote: > > On Tue 31-10-17 19:40:09, Tetsuo Handa wrote: > > > The reason I used __alloc_pages_slowpath() in alloc_pages_before_oomkill() is > > > to avoid duplicating code (such as checking for ALLOC_OOM and rebuilding zone > > > list) which needs to be maintained in sync with __alloc_pages_slowpath(). > > > > > > If you don't like calling __alloc_pages_slowpath() from > > > alloc_pages_before_oomkill(), I'm OK with calling __alloc_pages_nodemask() > > > (with __GFP_DIRECT_RECLAIM/__GFP_NOFAIL cleared and __GFP_NOWARN set), for > > > direct reclaim functions can call __alloc_pages_nodemask() (with PF_MEMALLOC > > > set in order to avoid recursion of direct reclaim). > > > > > > We are rebuilding zone list if selected as an OOM victim, for > > > __gfp_pfmemalloc_flags() returns ALLOC_OOM if oom_reserves_allowed(current) > > > is true. > > > > So your answer is copy&paste without a deeper understanding, righ? > > Right. I wanted to avoid duplicating code. > But I had to duplicate in order to allow OOM victims to try ALLOC_OOM. I absolutely hate this cargo cult programming! [...] > > While both have some merit, the first reason is mostly historical > > because we have the explicit locking now and it is really unlikely that > > the memory would be available right after we have given up trying. > > Last attempt allocation makes some sense of course but considering that > > the oom victim selection is quite an expensive operation which can take > > a considerable amount of time it makes much more sense to retry the > > allocation after the most expensive part rather than before. Therefore > > move the last attempt right before we are trying to kill an oom victim > > to rule potential races when somebody could have freed a lot of memory > > in the meantime. This will reduce the time window for potentially > > pre-mature OOM killing considerably. > > But this is about "doing last second allocation attempt after selecting > an OOM victim". This is not about "allowing OOM victims to try ALLOC_OOM > before selecting next OOM victim" which is the actual problem I'm trying > to deal with. then split it into two. First make the general case and then add a more sophisticated on top. Dealing with multiple issues at once is what makes all those brain cells suffer. -- Michal Hocko SUSE Labs -- 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>
