回复: Re: [PATCH] migrate_pages: modify max number of pages to migrate in batch

[李真能]

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主　题：Re: [PATCH] migrate_pages: modify max number of pages to migrate in batch
日　期：2024-06-25 09:17
发件人：ying.huang
收件人：李真能;

Hi, Zhenneng,

Zhenneng Li writes:

> We restrict the number of pages to be migrated to no more than
> HPAGE_PMD_NR or NR_MAX_BATCHED_MIGRATION, but in fact, the
> number of pages to be migrated may reach 2*HPAGE_PMD_NR-1 or 2
> *NR_MAX_BATCHED_MIGRATION-1, it's not in inconsistent with the context.

Yes. It's not HPAGE_PMD_NR exactly.

> Please refer to the patch: 42012e0436d4(migrate_pages: restrict number
> of pages to migrate in batch)
>
> Signed-off-by: Zhenneng Li
> ---
> mm/migrate.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 781979567f64..7a4b37aac9e8 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1961,7 +1961,7 @@ int migrate_pages(struct list_head *from, new_folio_t get_new_folio,
> break;
> }
> if (nr_pages >= NR_MAX_BATCHED_MIGRATION)
> - list_cut_before(&folios, from, &folio2->lru);
> + list_cut_before(&folios, from, &folio->lru);

If the first entry of the list "from" is a THP with size HPAGE_PMD_NR,
"folio" will be the first entry of from, so that "folios" will be empty.
Right?

 

Yes, It's right, so we can check whether it is the first entry of the list "from", new patch are as follows(attachment is patch file):

diff --git a/mm/migrate.c b/mm/migrate.c
index 781979567f64..cce8e2b85e89 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1957,11 +1957,12 @@ int migrate_pages(struct list_head *from, new_folio_t get_new_folio,
}

nr_pages += folio_nr_pages(folio);
- if (nr_pages >= NR_MAX_BATCHED_MIGRATION)
+ if ((nr_pages >= NR_MAX_BATCHED_MIGRATION) &&
+ (!list_first_entry(from, struct folio, lru)))
break;
}
if (nr_pages >= NR_MAX_BATCHED_MIGRATION)
- list_cut_before(&folios, from, &folio2->lru);
+ list_cut_before(&folios, from, &folio->lru);
else
list_splice_init(from, &folios);
if (mode == MIGRATE_ASYNC)

 

> else
> list_splice_init(from, &folios);
> if (mode == MIGRATE_ASYNC)

--
Best Regards,
Huang, Ying

Attachment: migrate_pages-modify-max-number-of-pages-to-migrate-in-batch.patch
Description: Binary data