On 16.08.24 17:06, Zi Yan wrote:
On 16 Aug 2024, at 7:30, Kefeng Wang wrote:
On 2024/8/16 18:11, David Hildenbrand wrote:
On 16.08.24 06:06, Kefeng Wang wrote:
The gigantic page size may larger than memory block size, so memory
offline always fails in this case after commit b2c9e2fbba32 ("mm: make
alloc_contig_range work at pageblock granularity"),
offline_pages
start_isolate_page_range
start_isolate_page_range(isolate_before=true)
isolate [isolate_start, isolate_start + pageblock_nr_pages)
start_isolate_page_range(isolate_before=false)
isolate [isolate_end - pageblock_nr_pages, isolate_end) pageblock
__alloc_contig_migrate_range
isolate_migratepages_range
isolate_migratepages_block
isolate_or_dissolve_huge_page
if (hstate_is_gigantic(h))
return -ENOMEM;
In fact, we don't need to migrate page in page range isolation, for
memory offline path, there is do_migrate_range() to move the pages.
For contig allocation, there is another __alloc_contig_migrate_range()
after isolation to migrate the pages. So fix issue by skipping the
__alloc_contig_migrate_range() in isolate_single_pageblock().
Fixes: b2c9e2fbba32 ("mm: make alloc_contig_range work at pageblock granularity")
Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
---
mm/page_isolation.c | 28 +++-------------------------
1 file changed, 3 insertions(+), 25 deletions(-)
diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index 39fb8c07aeb7..7e04047977cf 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -403,30 +403,8 @@ static int isolate_single_pageblock(unsigned long boundary_pfn, int flags,
unsigned long head_pfn = page_to_pfn(head);
unsigned long nr_pages = compound_nr(head);
- if (head_pfn + nr_pages <= boundary_pfn) {
- pfn = head_pfn + nr_pages;
- continue;
- }
-
-#if defined CONFIG_COMPACTION || defined CONFIG_CMA
- if (PageHuge(page)) {
- int page_mt = get_pageblock_migratetype(page);
- struct compact_control cc = {
- .nr_migratepages = 0,
- .order = -1,
- .zone = page_zone(pfn_to_page(head_pfn)),
- .mode = MIGRATE_SYNC,
- .ignore_skip_hint = true,
- .no_set_skip_hint = true,
- .gfp_mask = gfp_flags,
- .alloc_contig = true,
- };
- INIT_LIST_HEAD(&cc.migratepages);
-
- ret = __alloc_contig_migrate_range(&cc, head_pfn,
- head_pfn + nr_pages, page_mt);
- if (ret)
- goto failed;
But won't this break alloc_contig_range() then? I would have expected that you have to special-case here on the migration reason (MEMORY_OFFLINE).
Yes, this is what I did in rfc, only skip migration for offline path.
but Zi Yan suggested to remove migration totally[1]
[1] https://lore.kernel.org/linux-mm/50FEEE33-49CA-48B5-B4C5-964F1BE25D43@xxxxxxxxxx/
I remember some dirty details when we're trying to allcoate with a single pageblock for alloc_contig_range().
Most likely I was overthinking about the situation back then. I thought
I'm more than happy if we can remove that code here :)
PageHuge, PageLRU, and __PageMovable all can be bigger than a pageblock,
but in reality only PageHuge can and the gigantic PageHuge is freed as
order-0.
Does that still hold with Yu's patches to allocate/free gigantic pages
from CMA using compound pages that are on the list (and likely already
in mm-unstable)? I did not look at the freeing path of that patchset. As
the buddy doesn't understand anything larger than MAX_ORDER, I would
assume that we are fine.
I assume the real issue is when we have a movable allocation (folio)
that spans multiple pageblocks. For example, when MAX_ORDER is large
than a single pageblock, like it is on x86.
Besides gigantic pages, I wonder if that can happen. Likely currently
really only with hugetlb.
This means MIGRATE_ISOLATE pageblocks will get to the right
free list after __alloc_contig_migrate_range(), the one after
start_isolate_page_range().
David, I know we do not have cross-pageblock PageLRU yet (wait until
someone adds PMD-level mTHP). But I am not sure about __PageMovable,
even if you and Johannes told me that __PageMovable has no compound page.
I think it's all order-0. Likely we should sanity check that somewhere
(when setting a folio-page movable?).
For example, the vmware balloon handles 2M pages differently than 4k
pages. Only the latter is movable.
I wonder what are the use cases for __PageMovable. Is it possible for
a driver to mark its cross-pageblock page __PageMovable and provide
->isolate_page and ->migratepage in its struct address_space_operations?
Or it is unsupported, so I should not need to worry about it.
I never tried. We should document and enforce/sanity check that it only
works with order-0 for now.
Note that memory offlining always covers pageblocks large than MAX_ORDER chunks (which implies full pageblocks) but alloc_contig_range() + CMA might only cover (parts of) single pageblocks.
Hoping Zi Yan can review :)
At the moment, I think this is the right clean up.
I think we want to have some way to catch when it changes. For example,
can we warn if we find a LRU folio here that is large than a single
pageblock?
Also, I think we have to document why it works with hugetlb gigantic
folios / large CMA allocations somewhere (the order-0 stuff you note
above). Maybe as part of this changelog.
--
Cheers,
David / dhildenb
