On 05/15/2017 03:38 PM, Michal Hocko wrote:
On Mon 15-05-17 14:12:10, Pasha Tatashin wrote:
Hi Michal,
After looking at your suggested memblock_virt_alloc_core() change again, I
decided to keep what I have. I do not want to inline
memblock_virt_alloc_internal(), because it is not a performance critical
path, and by inlining it we will unnecessarily increase the text size on all
platforms.
I do not insist but I would really _prefer_ if the bool zero argument
didn't proliferate all over the memblock API.
Sure, I will remove zero boolean argument from
memblock_virt_alloc_internal(), and do memset() calls inside callers.
Also, because it will be very hard to make sure that no platform regresses
by making memset() default in _memblock_virt_alloc_core() (as I already
showed last week at least sun4v SPARC64 will require special changes in
order for this to work), I decided to make it available only for "deferred
struct page init" case. As, what is already in the patch.
I do not think this is the right approach. Your measurements just show
that sparc could have a more optimized memset for small sizes. If you
keep the same memset only for the parallel initialization then you
just hide this fact. I wouldn't worry about other architectures. All
sane architectures should simply work reasonably well when touching a
single or only few cache lines at the same time. If some arches really
suffer from small memsets then the initialization should be driven by a
specific ARCH_WANT_LARGE_PAGEBLOCK_INIT rather than making this depend
on DEFERRED_INIT. Or if you are too worried then make it opt-in and make
it depend on ARCH_WANT_PER_PAGE_INIT and make it enabled for x86 and
sparc after memset optimization.
OK, I will think about this.
I do not really like adding new configs because they tend to clutter the
code. This is why, I wanted to rely on already existing config that I
know benefits all platforms that use it. Eventually,
"CONFIG_DEFERRED_STRUCT_PAGE_INIT" is going to become the default
everywhere, as there should not be a drawback of using it even on small
machines.
Pasha
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