Messages in this thread | | | Date | Wed, 22 May 2019 11:19:04 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH 2/4] mm/vmap: preload a CPU with one object for split purpose |
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On Wed, 22 May 2019 17:09:37 +0200 "Uladzislau Rezki (Sony)" <urezki@gmail.com> wrote:
> Introduce ne_fit_preload()/ne_fit_preload_end() functions > for preloading one extra vmap_area object to ensure that > we have it available when fit type is NE_FIT_TYPE. > > The preload is done per CPU and with GFP_KERNEL permissive > allocation masks, which allow to be more stable under low > memory condition and high memory pressure.
What is the reason for this change? Presumably some workload is suffering from allocation failures? Please provide a full description of when and how this occurs so others can judge the desirability of this change.
> --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -364,6 +364,13 @@ static LIST_HEAD(free_vmap_area_list); > */ > static struct rb_root free_vmap_area_root = RB_ROOT; > > +/* > + * Preload a CPU with one object for "no edge" split case. The > + * aim is to get rid of allocations from the atomic context, thus > + * to use more permissive allocation masks. > + */ > +static DEFINE_PER_CPU(struct vmap_area *, ne_fit_preload_node); > + > static __always_inline unsigned long > va_size(struct vmap_area *va) > { > @@ -950,9 +957,24 @@ adjust_va_to_fit_type(struct vmap_area *va, > * L V NVA V R > * |---|-------|---| > */ > - lva = kmem_cache_alloc(vmap_area_cachep, GFP_NOWAIT); > - if (unlikely(!lva)) > - return -1; > + lva = __this_cpu_xchg(ne_fit_preload_node, NULL); > + if (unlikely(!lva)) { > + /* > + * For percpu allocator we do not do any pre-allocation > + * and leave it as it is. The reason is it most likely > + * never ends up with NE_FIT_TYPE splitting. In case of > + * percpu allocations offsets and sizes are aligned to > + * fixed align request, i.e. RE_FIT_TYPE and FL_FIT_TYPE > + * are its main fitting cases. > + * > + * There are few exceptions though, as en example it is
"a few"
s/en/an/
> + * a first allocation(early boot up) when we have "one"
s/(/ (/
> + * big free space that has to be split. > + */ > + lva = kmem_cache_alloc(vmap_area_cachep, GFP_NOWAIT); > + if (!lva) > + return -1; > + } > > /* > * Build the remainder. > @@ -1023,6 +1045,50 @@ __alloc_vmap_area(unsigned long size, unsigned long align, > } > > /* > + * Preload this CPU with one extra vmap_area object to ensure > + * that we have it available when fit type of free area is > + * NE_FIT_TYPE. > + * > + * The preload is done in non-atomic context thus, it allows us
s/ thus,/, thus/
> + * to use more permissive allocation masks, therefore to be more
s/, therefore//
> + * stable under low memory condition and high memory pressure. > + * > + * If success, it returns zero with preemption disabled. In case > + * of error, (-ENOMEM) is returned with preemption not disabled. > + * Note it has to be paired with alloc_vmap_area_preload_end(). > + */ > +static void > +ne_fit_preload(int *preloaded) > +{ > + preempt_disable(); > + > + if (!__this_cpu_read(ne_fit_preload_node)) { > + struct vmap_area *node; > + > + preempt_enable(); > + node = kmem_cache_alloc(vmap_area_cachep, GFP_KERNEL); > + if (node == NULL) { > + *preloaded = 0; > + return; > + } > + > + preempt_disable(); > + > + if (__this_cpu_cmpxchg(ne_fit_preload_node, NULL, node)) > + kmem_cache_free(vmap_area_cachep, node); > + } > + > + *preloaded = 1; > +}
Why not make it do `return preloaded;'? The pass-and-return-by-reference seems unnecessary?
Otherwise it all appears solid and sensible.
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