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SubjectRe: [PATCH v3 3/3] mm/vmalloc: add more comments to the adjust_va_to_fit_type()
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) <urezki@gmail.com>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
> 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

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