On 10/5/21 13:09, Michal Hocko wrote: > On Tue 05-10-21 11:20:51, Vlastimil Babka wrote: > [...] >> > --- a/include/linux/gfp.h >> > +++ b/include/linux/gfp.h >> > @@ -209,7 +209,11 @@ struct vm_area_struct; >> > * used only when there is no reasonable failure policy) but it is >> > * definitely preferable to use the flag rather than opencode endless >> > * loop around allocator. >> > - * Using this flag for costly allocations is _highly_ discouraged. >> > + * Use of this flag may lead to deadlocks if locks are held which would >> > + * be needed for memory reclaim, write-back, or the timely exit of a >> > + * process killed by the OOM-killer. Dropping any locks not absolutely >> > + * needed is advisable before requesting a %__GFP_NOFAIL allocate. >> > + * Using this flag for costly allocations (order>1) is _highly_ discouraged. >> >> We define costly as 3, not 1. But sure it's best to avoid even order>0 for >> __GFP_NOFAIL. Advising order>1 seems arbitrary though? > > This is not completely arbitrary. We have a warning for any higher order > allocation. > rmqueue: > WARN_ON_ONCE((gfp_flags & __GFP_NOFAIL) && (order > 1)); Oh, I missed that. > I do agree that "Using this flag for higher order allocations is > _highly_ discouraged. Well, with the warning in place this is effectively forbidden, not just discouraged. >> > */ >> > #define __GFP_IO ((__force gfp_t)___GFP_IO) >> > #define __GFP_FS ((__force gfp_t)___GFP_FS) >> > >> > >> > >
