Commit c9c510dc authored by David Hildenbrand's avatar David Hildenbrand Committed by Linus Torvalds

mm/page_alloc: tweak comments in has_unmovable_pages()

Patch series "mm / virtio-mem: support ZONE_MOVABLE", v5.

When introducing virtio-mem, the semantics of ZONE_MOVABLE were rather
unclear, which is why we special-cased ZONE_MOVABLE such that partially
plugged blocks would never end up in ZONE_MOVABLE.

Now that the semantics are much clearer (and are documented in patch #6),
let's support partially plugged memory blocks in ZONE_MOVABLE, allowing
partially plugged memory blocks to be online to ZONE_MOVABLE and also
unplugging from such memory blocks.  This avoids surprises when onlining
of memory blocks suddenly fails, just because they are not completely
populated by virtio-mem (yet).

This is especially helpful for testing, but also paves the way for
virtio-mem optimizations, allowing more memory to get reliably unplugged.

Cleanup has_unmovable_pages() and set_migratetype_isolate(), providing
better documentation of how ZONE_MOVABLE interacts with different kind of
unmovable pages (memory offlining vs.  alloc_contig_range()).

This patch (of 6):

Let's move the split comment regarding bootmem allocations and memory
holes, especially in the context of ZONE_MOVABLE, to the PageReserved()
check.
Signed-off-by: default avatarDavid Hildenbrand <david@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: default avatarBaoquan He <bhe@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Qian Cai <cai@lca.pw>
Link: http://lkml.kernel.org/r/20200816125333.7434-1-david@redhat.com
Link: http://lkml.kernel.org/r/20200816125333.7434-2-david@redhat.comSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent be4f1ae9
...@@ -8235,14 +8235,6 @@ struct page *has_unmovable_pages(struct zone *zone, struct page *page, ...@@ -8235,14 +8235,6 @@ struct page *has_unmovable_pages(struct zone *zone, struct page *page,
unsigned long iter = 0; unsigned long iter = 0;
unsigned long pfn = page_to_pfn(page); unsigned long pfn = page_to_pfn(page);
/*
* TODO we could make this much more efficient by not checking every
* page in the range if we know all of them are in MOVABLE_ZONE and
* that the movable zone guarantees that pages are migratable but
* the later is not the case right now unfortunatelly. E.g. movablecore
* can still lead to having bootmem allocations in zone_movable.
*/
if (is_migrate_cma_page(page)) { if (is_migrate_cma_page(page)) {
/* /*
* CMA allocations (alloc_contig_range) really need to mark * CMA allocations (alloc_contig_range) really need to mark
...@@ -8261,6 +8253,12 @@ struct page *has_unmovable_pages(struct zone *zone, struct page *page, ...@@ -8261,6 +8253,12 @@ struct page *has_unmovable_pages(struct zone *zone, struct page *page,
page = pfn_to_page(pfn + iter); page = pfn_to_page(pfn + iter);
/*
* Both, bootmem allocations and memory holes are marked
* PG_reserved and are unmovable. We can even have unmovable
* allocations inside ZONE_MOVABLE, for example when
* specifying "movablecore".
*/
if (PageReserved(page)) if (PageReserved(page))
return page; return page;
...@@ -8334,14 +8332,6 @@ struct page *has_unmovable_pages(struct zone *zone, struct page *page, ...@@ -8334,14 +8332,6 @@ struct page *has_unmovable_pages(struct zone *zone, struct page *page,
* it. But now, memory offline itself doesn't call * it. But now, memory offline itself doesn't call
* shrink_node_slabs() and it still to be fixed. * shrink_node_slabs() and it still to be fixed.
*/ */
/*
* If the page is not RAM, page_count()should be 0.
* we don't need more check. This is an _used_ not-movable page.
*
* The problematic thing here is PG_reserved pages. PG_reserved
* is set to both of a memory hole page and a _used_ kernel
* page at boot.
*/
return page; return page;
} }
return NULL; return NULL;
......
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