On 17.07.23 17:41, Ryan Roberts wrote:
On 17/07/2023 16:30, Matthew Wilcox wrote:
On Mon, Jul 17, 2023 at 03:31:08PM +0100, Ryan Roberts wrote:
In preparation for the introduction of large folios for anonymous
memory, we would like to be able to split them when they have unmapped
subpages, in order to free those unused pages under memory pressure. So
remove the artificial requirement that the large folio needed to be at
least PMD-sized.
Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx>
Reviewed-by: Yu Zhao <yuzhao@xxxxxxxxxx>
Reviewed-by: Yin Fengwei <fengwei.yin@xxxxxxxxx>
Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Thanks!
*/
- if (folio_test_pmd_mappable(folio) && folio_test_anon(folio))
+ if (folio_test_large(folio) && folio_test_anon(folio))
if (!compound || nr < nr_pmdmapped)
deferred_split_folio(folio);
I wonder if it's worth introducing a folio_test_deferred_split() (better
naming appreciated ...) to allow us to allocate order-1 folios and not
do horrible things. Maybe it's not worth supporting order-1 folios;
we're always better off going to order-2 immediately. Just thinking.
There is more than just _deferred_list in the 3rd page; you also have _flags_2a
and _head_2a. I guess you know much better than me what they store. But I'm
guessing its harder than jsut not splitting an order-1 page?
With the direction of large anon folios (_not_ retrying with every order down to
0), I'm not sure what the use case would be for order-1 anyway?
Just noting that we might need some struct-page space for better
mapcount/shared tracking, which might get hard for order-1 pages.
--
Cheers,
David / dhildenb
