On Wed 16-10-19 11:54:38, Uladzislau Rezki (Sony) wrote: > When fit type is NE_FIT_TYPE there is a need in one extra object. > Usually the "ne_fit_preload_node" per-CPU variable has it and > there is no need in GFP_NOWAIT allocation, but there are exceptions. > > This commit just adds more explanations, as a result giving > answers on questions like when it can occur, how often, under > which conditions and what happens if GFP_NOWAIT gets failed. > > Signed-off-by: Uladzislau Rezki (Sony) <[email protected]>
Acked-by: Michal Hocko <[email protected]> > --- > mm/vmalloc.c | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index 593bf554518d..2290a0d270e4 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -969,6 +969,19 @@ adjust_va_to_fit_type(struct vmap_area *va, > * There are a few exceptions though, as an example it > is > * a first allocation (early boot up) when we have "one" > * big free space that has to be split. > + * > + * Also we can hit this path in case of regular "vmap" > + * allocations, if "this" current CPU was not preloaded. > + * See the comment in alloc_vmap_area() why. If so, then > + * GFP_NOWAIT is used instead to get an extra object for > + * split purpose. That is rare and most time does not > + * occur. > + * > + * What happens if an allocation gets failed. Basically, > + * an "overflow" path is triggered to purge lazily freed > + * areas to free some memory, then, the "retry" path is > + * triggered to repeat one more time. See more details > + * in alloc_vmap_area() function. > */ > lva = kmem_cache_alloc(vmap_area_cachep, GFP_NOWAIT); > if (!lva) > -- > 2.20.1 > -- Michal Hocko SUSE Labs
