On Fri, Jul 3, 2020 at 9:14 AM Muchun Song <songmuchun@xxxxxxxxxxxxx> wrote:
>
> When we are in the interrupt context, it is irrelevant to the
> current task context. If we use current task's mems_allowed, we
> can fair to alloc pages in the fast path and fall back to slow
> path memory allocation when the current node(which is the current
> task mems_allowed) does not have enough memory to allocate. In
> this case, it slows down the memory allocation speed of interrupt
> context. So we can skip setting the nodemask to allow any node
> to allocate memory, so that fast path allocation can success.
>
> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> ---
> mm/page_alloc.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index b48336e20bdcd..a6c36cd557d1d 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4726,10 +4726,12 @@ static inline bool prepare_alloc_pages(gfp_t gfp_mask, unsigned int order,
>
> if (cpusets_enabled()) {
> *alloc_mask |= __GFP_HARDWALL;
> - if (!ac->nodemask)
> - ac->nodemask = &cpuset_current_mems_allowed;
> - else
> + if (!ac->nodemask) {
> + if (!in_interrupt())
> + ac->nodemask = &cpuset_current_mems_allowed;
If !ac->nodemask and in_interrupt() the ALLOC_CPUSET flag is not set,
which by-passes the __cpuset_zone_allowed() check for allocations.
This works fine because in the case if in_interrupt() the function
allows allocation on any zone/node.
> + } else {
> *alloc_flags |= ALLOC_CPUSET;
> + }
> }
However, if you write the condition as follows:
if (cpusets_enabled()) {
*alloc_mask |= __GFP_HARDWALL;
if (!in_interrupt() && !ac->nodemask)
ac->nodemask = &cpuset_current_mems_allowed;
else
*alloc_flags |= ALLOC_CPUSET;
}
then the code is future-proof in case of __cpuset_zone_allowed() is
one day extended to support IRQ context too (it probably should
eventually respect IRQ SMP affinity).
>
> fs_reclaim_acquire(gfp_mask);
> --
> 2.11.0
>
>
