On 9/17/21 04:56, NeilBrown wrote: > __GFP_NOFAIL is documented both in gfp.h and memory-allocation.rst. > The details are not entirely consistent. > > This patch ensures both places state that: > - there is a risk of deadlock with reclaim/writeback/oom-kill > - it should only be used when there is no real alternative > - it is preferable to an endless loop > - it is strongly discourages for costly-order allocations. > > Signed-off-by: NeilBrown <neilb@xxxxxxx> Acked-by: Vlastimil Babka <vbabka@xxxxxxx> Nit below: > diff --git a/include/linux/gfp.h b/include/linux/gfp.h > index 55b2ec1f965a..1d2a89e20b8b 100644 > --- 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? > */ > #define __GFP_IO ((__force gfp_t)___GFP_IO) > #define __GFP_FS ((__force gfp_t)___GFP_FS) > > >
