On 8/9/22 19:18, Matthew Wilcox (Oracle) wrote:
Since slab does not use the page refcount, it can allocate and
free frozen pages, saving one atomic operation per free.
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Reviewed-by: William Kucharski <william.kucharski@xxxxxxxxxx>
AFAICS the problem of has_unmovable_pages() is not addressed:
https://lore.kernel.org/all/40d658da-6220-e05e-ba0b-d95c82f6bfb3@xxxxxxxxxx/
But I don't think it's sustainable approach to enhance the checks there
with PageSlab() and then with whatever other user will adopt allocating
frozen pages in the future. I guess it would be better to just be able
to detect pages on pcplist without false positives. A new page type?
Maybe the overhead of managing it would be negligible as we set
page->index anyway for migratetype?
---
mm/slab.c | 23 +++++++++++------------
1 file changed, 11 insertions(+), 12 deletions(-)
diff --git a/mm/slab.c b/mm/slab.c
index 10e96137b44f..e7603d23c6c9 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1355,23 +1355,23 @@ slab_out_of_memory(struct kmem_cache *cachep, gfp_t gfpflags, int nodeid)
static struct slab *kmem_getpages(struct kmem_cache *cachep, gfp_t flags,
int nodeid)
{
- struct folio *folio;
+ struct page *page;
struct slab *slab;
flags |= cachep->allocflags;
- folio = (struct folio *) __alloc_pages_node(nodeid, flags, cachep->gfporder);
- if (!folio) {
+ page = __alloc_frozen_pages(flags, cachep->gfporder, nodeid, NULL);
+ if (!page) {
slab_out_of_memory(cachep, flags, nodeid);
return NULL;
}
- slab = folio_slab(folio);
+ __SetPageSlab(page);
+ slab = (struct slab *)page;
account_slab(slab, cachep->gfporder, cachep, flags);
- __folio_set_slab(folio);
/* Record if ALLOC_NO_WATERMARKS was set when allocating the slab */
- if (sk_memalloc_socks() && page_is_pfmemalloc(folio_page(folio, 0)))
+ if (sk_memalloc_socks() && page_is_pfmemalloc(page))
slab_set_pfmemalloc(slab);
return slab;
@@ -1383,18 +1383,17 @@ static struct slab *kmem_getpages(struct kmem_cache *cachep, gfp_t flags,
static void kmem_freepages(struct kmem_cache *cachep, struct slab *slab)
{
int order = cachep->gfporder;
- struct folio *folio = slab_folio(slab);
+ struct page *page = (struct page *)slab;
- BUG_ON(!folio_test_slab(folio));
__slab_clear_pfmemalloc(slab);
- __folio_clear_slab(folio);
- page_mapcount_reset(folio_page(folio, 0));
- folio->mapping = NULL;
+ __ClearPageSlab(page);
+ page_mapcount_reset(page);
+ page->mapping = NULL;
if (current->reclaim_state)
current->reclaim_state->reclaimed_slab += 1 << order;
unaccount_slab(slab, order, cachep);
- __free_pages(folio_page(folio, 0), order);
+ free_frozen_pages(page, order);
}
static void kmem_rcu_free(struct rcu_head *head)
