On Tue, Oct 10, 2023 at 05:12:01PM -0400, Johannes Weiner wrote:
> On Mon, Oct 02, 2023 at 10:26:44PM -0400, Zi Yan wrote:
> > @@ -1614,10 +1652,43 @@ static int move_freepages(struct zone *zone, unsigned long start_pfn,
> >
> > order = buddy_order(page);
> > move_to_free_list(page, zone, order, old_mt, new_mt);
> > + /*
> > + * set page migratetype 1) only after we move all free pages in
> > + * one pageblock and 2) for all pageblocks within the page.
> > + *
> > + * for 1), since move_to_free_list() checks page migratetype with
> > + * old_mt and changing one page migratetype affects all pages
> > + * within the same pageblock, if we are moving more than
> > + * one free pages in the same pageblock, setting migratetype
> > + * right after first move_to_free_list() triggers the warning
> > + * in the following move_to_free_list().
> > + *
> > + * for 2), when a free page order is greater than pageblock_order,
> > + * all pageblocks within the free page need to be changed after
> > + * move_to_free_list().
>
> I think this can be somewhat simplified.
>
> There are two assumptions we can make. Buddies always consist of 2^n
> pages. And buddies and pageblocks are naturally aligned. This means
> that if this pageblock has the start of a buddy that straddles into
> the next pageblock(s), it must be the first page in the block. That in
> turn means we can move the handling before the loop.
Eh, scratch that. Obviously, a sub-block buddy can straddle blocks :(
So forget about my version of move_free_pages(). Only consider the
changes to find_straddling_buddy() and my question about multiple
blocks inside the requested range.
But I do have another question about your patch then. Say you have an
order-1 buddy that straddles into the block:
+ /* split at start_pfn if it is in the middle of a free page */
+ if (new_start_pfn != start_pfn && PageBuddy(pfn_to_page(new_start_pfn))) {
+ struct page *new_page = pfn_to_page(new_start_pfn);
+ int new_page_order = buddy_order(new_page);
+
+ if (new_start_pfn + (1 << new_page_order) > start_pfn) {
+ /* change migratetype so that split_free_page can work */
+ set_pageblock_migratetype(pfn_to_page(start_pfn), new_mt);
+ split_free_page(new_page, buddy_order(new_page),
+ start_pfn - new_start_pfn);
+
+ mt_changed_pfn = start_pfn;
+ /* move to next page */
+ start_pfn = new_start_pfn + (1 << new_page_order);
+ }
+ }
this will have changed the type of the block to new_mt.
But then the buddy scan will do this:
move_to_free_list(page, zone, order, old_mt, new_mt);
+ /*
+ * set page migratetype 1) only after we move all free pages in
+ * one pageblock and 2) for all pageblocks within the page.
+ *
+ * for 1), since move_to_free_list() checks page migratetype with
+ * old_mt and changing one page migratetype affects all pages
+ * within the same pageblock, if we are moving more than
+ * one free pages in the same pageblock, setting migratetype
+ * right after first move_to_free_list() triggers the warning
+ * in the following move_to_free_list().
+ *
+ * for 2), when a free page order is greater than pageblock_order,
+ * all pageblocks within the free page need to be changed after
+ * move_to_free_list().
That move_to_free_list() will complain that the pages no longer match
old_mt, no?
