On Wed 07-06-17 10:10:36, Wei Yang wrote: [...] > Hmm... Let me be more specific. With two factors, costly or not, flag set or > not, we have four combinations. Here it is classified into two categories. > > 1. __GFP_RETRY_MAYFAIL not set > > Brief description on behavior: > costly: pick up the shortcut, so no OOM > !costly: no shortcut and will OOM I think > > Impact from this patch set: > No. true > My personal understanding: > The allocation without __GFP_RETRY_MAYFAIL is not effected by this patch > set. Since !costly allocation will trigger OOM, this is the reason why > "small allocations never fail _practically_", as mentioned in > https://lwn.net/Articles/723317/. > > > 3. __GFP_RETRY_MAYFAIL set > > Brief description on behavior: > costly/!costly: no shortcut here and no OOM invoked > > Impact from this patch set: > For those allocations with __GFP_RETRY_MAYFAIL, OOM is not invoked for > both. yes > My personal understanding: > This is the semantic you are willing to introduce in this patch set. By > cutting off the OOM invoke when __GFP_RETRY_MAYFAIL is set, you makes this > a middle situation between NOFAIL and NORETRY. yes > page_alloc will try some luck to get some free pages without disturb other > part of the system. By doing so, the never fail allocation for !costly > pages will be "fixed". If I understand correctly, you are willing to make > this the default behavior in the future? I do not think we can make this a default in a foreseeable future unfortunately. That's why I've made it a gfp modifier in the first place. I assume many users will opt in by using the flag. In future we can even help by adding a highlevel GFP_$FOO flag but I am worried that this would just add to the explosion of existing highlevel gfp masks (e.g. do we want GFP_NOFS_MAY_FAIL, GFP_USER_MAY_FAIL, GFP_USER_HIGH_MOVABLE_MAYFAIL etc...) -- 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>
