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SubjectRe: [PATCH 6/7] hugetlb: hugepage migration core
On Tue, Jul 06, 2010 at 11:00:27AM -0500, Christoph Lameter wrote:
> On Fri, 2 Jul 2010, Naoya Horiguchi wrote:
>
> > --- v2.6.35-rc3-hwpoison/mm/migrate.c
> > +++ v2.6.35-rc3-hwpoison/mm/migrate.c
> > @@ -32,6 +32,7 @@
> > #include <linux/security.h>
> > #include <linux/memcontrol.h>
> > #include <linux/syscalls.h>
> > +#include <linux/hugetlb.h>
> > #include <linux/gfp.h>
> >
> > #include "internal.h"
> > @@ -74,6 +75,8 @@ void putback_lru_pages(struct list_head *l)
> > struct page *page2;
> >
> > list_for_each_entry_safe(page, page2, l, lru) {
> > + if (PageHuge(page))
> > + break;
> > list_del(&page->lru);
>
> Argh. Hugepages in putpack_lru_pages()? Huge pages are not on the lru.
> Come up with something cleaner here.

OK.

> > @@ -267,7 +284,14 @@ static int migrate_page_move_mapping(struct address_space *mapping,
> > * Note that anonymous pages are accounted for
> > * via NR_FILE_PAGES and NR_ANON_PAGES if they
> > * are mapped to swap space.
> > + *
> > + * Not account hugepage here for now because hugepage has
> > + * separate accounting rule.
> > */
> > + if (PageHuge(newpage)) {
> > + spin_unlock_irq(&mapping->tree_lock);
> > + return 0;
> > + }
> > __dec_zone_page_state(page, NR_FILE_PAGES);
> > __inc_zone_page_state(newpage, NR_FILE_PAGES);
> > if (PageSwapBacked(page)) {
>
> This looks wrong here. Too many special casing added to basic migration
> functionality.

Agreed.
As I replied in another email, I'll move to migrate_huge_page() and
avoid adding ugly changes like this.

> > @@ -284,7 +308,17 @@ static int migrate_page_move_mapping(struct address_space *mapping,
> > */
> > static void migrate_page_copy(struct page *newpage, struct page *page)
> > {
> > - copy_highpage(newpage, page);
> > + int i;
> > + struct hstate *h;
> > + if (!PageHuge(newpage))
> > + copy_highpage(newpage, page);
> > + else {
> > + h = page_hstate(newpage);
> > + for (i = 0; i < pages_per_huge_page(h); i++) {
> > + cond_resched();
> > + copy_highpage(newpage + i, page + i);
> > + }
> > + }
> >
> > if (PageError(page))
> > SetPageError(newpage);
>
> Could you generalize this for migrating an order N page?

Yes.
I'll define a helper function to handle order N case.

> > @@ -718,6 +752,11 @@ unlock:
> > put_page(page);
> >
> > if (rc != -EAGAIN) {
> > + if (PageHuge(newpage)) {
> > + put_page(newpage);
> > + goto out;
> > + }
> > +
>
> I dont like this kind of inconsistency with the refcounting. Page
> migration is complicated enough already.

OK.

Thanks,
Naoya Horiguchi


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