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SubjectRe: [RFC] memory hotremove patch take 2 [04/10] (isolate all free pages)
On Thu, 10 May 2007 17:42:54 +0100 (IST)
Mel Gorman <mel@csn.ul.ie> wrote:

> > + if (!pfn_valid(pfn))
> > + return -EINVAL;
>
> This may lead to boundary cases where pages cannot be captured at the
> start and end of non-aligned zones due to memory holes.
>
Hm, ok. maybe we can remove this.

> > + zone = info->zone;
> > + if ((zone != page_zone(pfn_to_page(pfn))) ||
> > + (zone != page_zone(pfn_to_page(last_pfn))))
> > + return -EINVAL;
>
> Is this check really necessary? Surely a caller to
> capture_isolate_freed_pages() will have already made all the necessary
> checks when adding the struct insolation_info ?
>
just because isolation_info is treated per zone.
Maybe MIGRATE_ISOLATING can allow us more flexible approach.


> > + drain_all_pages();
> > + spin_lock(&zone->lock);
> > + while (pfn < info->end_pfn) {
> > + if (!pfn_valid(pfn)) {
> > + pfn++;
> > + continue;
> > + }
> > + page = pfn_to_page(pfn);
> > + /* See page_is_buddy() */
> > + if (page_count(page) == 0 && PageBuddy(page)) {
>
> If PageBuddy is set it's free, you shouldn't have to check the page_count.
>
ok.

> > + order = page_order(page);
> > + order_size = 1 << order;
> > + zone->free_area[order].nr_free--;
> > + __mod_zone_page_state(zone, NR_FREE_PAGES, -order_size);
> > + list_del(&page->lru);
> > + rmv_page_order(page);
> > + isolate_page_nolock(info, page, order);
> > + nr_pages += order_size;
> > + pfn += order_size;
> > + } else {
> > + pfn++;
> > + }
> > + }
> > + spin_unlock(&zone->lock);
> > + return nr_pages;
> > +}
> > #endif /* CONFIG_PAGE_ISOLATION */
> >
>
> This is all similar to move_freepages() other than the locking part. It
> would be worth checking if there is code that could be shared or at least
> have similar styles.

Thank you, I'll look into move_freepages().

-Kame


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