Hello,
On Tue, 19 Mar 2024 11:47:53 -0400 Zi Yan <zi.yan@xxxxxxxx> wrote:
> From: Zi Yan <ziy@xxxxxxxxxx>
>
> If the source folio is on deferred split list, it is likely some subpages
> are not used. Split it before migration to avoid migrating unused subpages.
>
> Commit 616b8371539a6 ("mm: thp: enable thp migration in generic path")
> did not check if a THP is on deferred split list before migration, thus,
> the destination THP is never put on deferred split list even if the source
> THP might be. The opportunity of reclaiming free pages in a partially
> mapped THP during deferred list scanning is lost, but no other harmful
> consequence is present[1].
>
> From v2:
> 1. Split the source folio instead of migrating it (per Matthew Wilcox)[2].
>
> From v1:
> 1. Used dst to get correct deferred split list after migration
> (per Ryan Roberts).
>
> [1]: https://lore.kernel.org/linux-mm/03CE3A00-917C-48CC-8E1C-6A98713C817C@xxxxxxxxxx/
> [2]: https://lore.kernel.org/linux-mm/Ze_P6xagdTbcu1Kz@xxxxxxxxxxxxxxxxxxxx/
>
> Fixes: 616b8371539a ("mm: thp: enable thp migration in generic path")
> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
> ---
> mm/huge_memory.c | 22 ------------------
> mm/internal.h | 23 +++++++++++++++++++
> mm/migrate.c | 60 +++++++++++++++++++++++++++++++++++++++---------
> 3 files changed, 72 insertions(+), 33 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 9859aa4f7553..c6d4d0cdf4b3 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -766,28 +766,6 @@ pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
> return pmd;
> }
>
> -#ifdef CONFIG_MEMCG
> -static inline
> -struct deferred_split *get_deferred_split_queue(struct folio *folio)
> -{
> - struct mem_cgroup *memcg = folio_memcg(folio);
> - struct pglist_data *pgdat = NODE_DATA(folio_nid(folio));
> -
> - if (memcg)
> - return &memcg->deferred_split_queue;
> - else
> - return &pgdat->deferred_split_queue;
> -}
> -#else
> -static inline
> -struct deferred_split *get_deferred_split_queue(struct folio *folio)
> -{
> - struct pglist_data *pgdat = NODE_DATA(folio_nid(folio));
> -
> - return &pgdat->deferred_split_queue;
> -}
> -#endif
> -
> void folio_prep_large_rmappable(struct folio *folio)
> {
> if (!folio || !folio_test_large(folio))
> diff --git a/mm/internal.h b/mm/internal.h
> index d1c69119b24f..8fa36e84463a 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -1107,6 +1107,29 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
> unsigned long addr, pmd_t *pmd,
> unsigned int flags);
>
> +#ifdef CONFIG_MEMCG
> +static inline
> +struct deferred_split *get_deferred_split_queue(struct folio *folio)
> +{
> + struct mem_cgroup *memcg = folio_memcg(folio);
> + struct pglist_data *pgdat = NODE_DATA(folio_nid(folio));
> +
> + if (memcg)
> + return &memcg->deferred_split_queue;
> + else
> + return &pgdat->deferred_split_queue;
> +}
> +#else
> +static inline
> +struct deferred_split *get_deferred_split_queue(struct folio *folio)
> +{
> + struct pglist_data *pgdat = NODE_DATA(folio_nid(folio));
> +
> + return &pgdat->deferred_split_queue;
> +}
> +#endif
I found this breaks the build when CONFIG_TRANSPARENT_HUGEPAGE is not set, with
below error:
.../lib/../mm/internal.h: In function 'get_deferred_split_queue':
.../lib/../mm/internal.h:1127:22: error: 'struct pglist_data' has no member named 'deferred_split_queue'
1127 | return &pgdat->deferred_split_queue;
| ^~
Since the code was in hugepage.c, maybe the above chunk need to be wrapped by
#ifdef CONFIG_TRANSPARENT_HUGEPAGE? I confirmed below change is fixing the
build on my setup.
Thanks,
SJ
[...]
-------------------------------------- >8 -------------------------------------
diff --git a/mm/internal.h b/mm/internal.h
index dce2b9f5e6cd..fe9f69ceb140 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1106,6 +1106,7 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
unsigned long addr, pmd_t *pmd,
unsigned int flags);
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
#ifdef CONFIG_MEMCG
static inline
struct deferred_split *get_deferred_split_queue(struct folio *folio)
@@ -1126,7 +1127,8 @@ struct deferred_split *get_deferred_split_queue(struct folio *folio)
return &pgdat->deferred_split_queue;
}
-#endif
+#endif /* CONFIG_MEMCG */
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
/*
