On 27.08.24 17:35, Kefeng Wang wrote:
On 2024/8/27 23:10, David Hildenbrand wrote:
On 27.08.24 03:26, Kefeng Wang wrote:
On 2024/8/26 22:55, David Hildenbrand wrote:
On 17.08.24 10:49, Kefeng Wang wrote:
Use the isolate_folio_to_list() to unify hugetlb/LRU/non-LRU
folio isolation, which cleanup code a bit and save a few calls
to compound_head().
Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
---
...
Hm, remind me why we are changing the hugetlb code to not take a
reference here? It does look odd.
Different from folio_isolate_lru(), isolate_hugetlb() will check folio
and try get a reference of folio after get hugetlb_lock, other hugetlb
operation protected by this big lock too, so no need to take a reference
here.
But this hugetlb-special casing looks quite ... special TBH.
Is there no way to avoid it?
I'd prefer something like the following, with a comment
if (hugetlb)
/*
* We also want to migrate hugetlb folios that span multiple
* memory blocks. So use whatever head page we identified.
*/
folio = folio_try_get(folio);
else
folio = folio_get_nontail_page(page);
if (!folio)
continue;
And then just dropping the reference unconditionally.
Is there a problem with that? Optimizing for hugetlb references during
migration is not worth the trouble.
But now I wonder, why we not simply unconditionally do a folio_try_get()
Yes, I use folio_get_nontail_page() and folio_put() unconditionally in v1,
Yes, that part I remember.
this will skip tail page, not consistent with previous behavior for
hugetlb, so I change to current way, but for migration, use
folio_try_get()/folio_put() is enough since we always migrate the whole
folio, it will be more simple.
I'm wondering if anything relies on the folio_get_nontail_page() part,
but I cannot really think "what" that should be. Using folio_try_get()
would be much simpler: we have a page, we want to migrate it away, to do
that we have to migrate the folio (wherever that starts or ends).
Also, make sure to test with free hugetlb folios.
I will push an additional fix to v3,
which just sent a couple of hours ago.
Feel free to send a fixup for v2 instead.
--
Cheers,
David / dhildenb
