On Thu, Jan 28, 2016 at 09:40:03PM +0100, Michal Hocko wrote: > From: Michal Hocko <mhocko@xxxxxxxx> > > __alloc_pages_may_oom has been doing get_page_from_freelist with > ALLOC_WMARK_HIGH target before going out_of_memory and invoking the oom > killer. This has two reasons as explained by Andrea: > " > : the reason for the high wmark is to reduce the likelihood of livelocks > : and be sure to invoke the OOM killer, if we're still under pressure > : and reclaim just failed. The high wmark is used to be sure the failure > : of reclaim isn't going to be ignored. If using the min wmark like > : you propose there's risk of livelock or anyway of delayed OOM killer > : invocation. > : > : The reason for doing one last wmark check (regardless of the wmark > : used) before invoking the oom killer, was just to be sure another OOM > : killer invocation hasn't already freed a ton of memory while we were > : stuck in reclaim. A lot of free memory generated by the OOM killer, > : won't make a parallel reclaim more likely to succeed, it just creates > : free memory, but reclaim only succeeds when it finds "freeable" memory > : and it makes progress in converting it to free memory. So for the > : purpose of this last check, the high wmark would work fine as lots of > : free memory would have been generated in such case. > " > > This is no longer a concern after "mm, oom: rework oom detection" > because should_reclaim_retry performs the water mark check right before > __alloc_pages_may_oom is invoked. Remove the last moment allocation > request as it just makes the code more confusing and doesn't really > serve any purpose because a success is basically impossible otherwise > should_reclaim_retry would force the reclaim to retry. So this is > merely a code cleanup rather than a functional change. > > Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> The check has to happen while holding the OOM lock, otherwise we'll end up killing much more than necessary when there are many racing allocations. Please drop this patch. -- 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>