On 2018-10-10 23:03, Michal Hocko wrote:
On Wed 10-10-18 22:26:41, Arun KS wrote:
On 2018-10-10 21:00, Vlastimil Babka wrote:
> On 10/5/18 10:10 AM, Arun KS wrote:
> > When free pages are done with higher order, time spend on
> > coalescing pages by buddy allocator can be reduced. With
> > section size of 256MB, hot add latency of a single section
> > shows improvement from 50-60 ms to less than 1 ms, hence
> > improving the hot add latency by 60%. Modify external
> > providers of online callback to align with the change.
> >
> > Signed-off-by: Arun KS <arunks@xxxxxxxxxxxxxx>
>
> [...]
>
> > @@ -655,26 +655,44 @@ void __online_page_free(struct page *page)
> > }
> > EXPORT_SYMBOL_GPL(__online_page_free);
> >
> > -static void generic_online_page(struct page *page)
> > +static int generic_online_page(struct page *page, unsigned int order)
> > {
> > - __online_page_set_limits(page);
>
> This is now not called anymore, although the xen/hv variants still do
> it. The function seems empty these days, maybe remove it as a followup
> cleanup?
>
> > - __online_page_increment_counters(page);
> > - __online_page_free(page);
> > + __free_pages_core(page, order);
> > + totalram_pages += (1UL << order);
> > +#ifdef CONFIG_HIGHMEM
> > + if (PageHighMem(page))
> > + totalhigh_pages += (1UL << order);
> > +#endif
>
> __online_page_increment_counters() would have used
> adjust_managed_page_count() which would do the changes under
> managed_page_count_lock. Are we safe without the lock? If yes, there
> should perhaps be a comment explaining why.
Looks unsafe without managed_page_count_lock.
Why does it matter actually? We cannot online/offline memory in
parallel. This is not the case for the boot where we initialize memory
in parallel on multiple nodes. So this seems to be safe currently
unless
I am missing something. A comment explaining that would be helpful
though.
Other main callers of adjust_manage_page_count(),
static inline void free_reserved_page(struct page *page)
{
__free_reserved_page(page);
adjust_managed_page_count(page, 1);
}
static inline void mark_page_reserved(struct page *page)
{
SetPageReserved(page);
adjust_managed_page_count(page, -1);
}
Won't they race with memory hotplug?
Few more,
./drivers/xen/balloon.c:519: adjust_managed_page_count(page,
-1);
./drivers/virtio/virtio_balloon.c:175: adjust_managed_page_count(page,
-1);
./drivers/virtio/virtio_balloon.c:196: adjust_managed_page_count(page,
1);
./mm/hugetlb.c:2158: adjust_managed_page_count(page,
1 << h->order);
Regards,
Arun
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