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Message-ID: <081dc7bb-ae60-4a38-b9c8-560280cf5cf8@linux.alibaba.com>
Date: Tue, 12 Mar 2024 15:27:12 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Zi Yan <ziy@...dia.com>, linux-mm@...ck.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
"Matthew Wilcox (Oracle)" <willy@...radead.org>,
Yang Shi <shy828301@...il.com>, Huang Ying <ying.huang@...el.com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
Ryan Roberts <ryan.roberts@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm/migrate: put dest folio on deferred split list if
source was there.
On 2024/3/12 03:58, Zi Yan wrote:
> From: Zi Yan <ziy@...dia.com>
>
> 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]. Checking source folio deferred split list
> status before page unmapped and add destination folio to the list if
> source was after migration.
>
> [1]: https://lore.kernel.org/linux-mm/03CE3A00-917C-48CC-8E1C-6A98713C817C@nvidia.com/
>
> From v1:
> 1. Used dst to get correct deferred split list after migration
> (per Ryan Roberts).
>
> Fixes: 616b8371539a ("mm: thp: enable thp migration in generic path")
> Signed-off-by: Zi Yan <ziy@...dia.com>
> ---
> mm/huge_memory.c | 22 ----------------------
> mm/internal.h | 23 +++++++++++++++++++++++
> mm/migrate.c | 26 +++++++++++++++++++++++++-
> 3 files changed, 48 insertions(+), 23 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
> +
> +
> /*
> * mm/mmap.c
> */
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 73a052a382f1..591e65658535 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -20,6 +20,7 @@
> #include <linux/pagemap.h>
> #include <linux/buffer_head.h>
> #include <linux/mm_inline.h>
> +#include <linux/mmzone.h>
> #include <linux/nsproxy.h>
> #include <linux/ksm.h>
> #include <linux/rmap.h>
> @@ -1037,7 +1038,10 @@ static int move_to_new_folio(struct folio *dst, struct folio *src,
> enum {
> PAGE_WAS_MAPPED = BIT(0),
> PAGE_WAS_MLOCKED = BIT(1),
> - PAGE_OLD_STATES = PAGE_WAS_MAPPED | PAGE_WAS_MLOCKED,
> + PAGE_WAS_ON_DEFERRED_LIST = BIT(2),
> + PAGE_OLD_STATES = PAGE_WAS_MAPPED |
> + PAGE_WAS_MLOCKED |
> + PAGE_WAS_ON_DEFERRED_LIST,
> };
>
> static void __migrate_folio_record(struct folio *dst,
> @@ -1168,6 +1172,17 @@ static int migrate_folio_unmap(new_folio_t get_new_folio,
> folio_lock(src);
> }
> locked = true;
> + if (folio_test_large_rmappable(src) &&
IMO, you should check folio_test_large() before calling
folio_test_large_rmappable(), since the PG_large_rmappable flag is
stored in the first tail page.
> + !list_empty(&src->_deferred_list)) {
> + struct deferred_split *ds_queue = get_deferred_split_queue(src);
> +
> + spin_lock(&ds_queue->split_queue_lock);
> + ds_queue->split_queue_len--;
> + list_del_init(&src->_deferred_list);
> + spin_unlock(&ds_queue->split_queue_lock);
> + old_page_state |= PAGE_WAS_ON_DEFERRED_LIST;
> + }
> +
> if (folio_test_mlocked(src))
> old_page_state |= PAGE_WAS_MLOCKED;
>
> @@ -1307,6 +1322,15 @@ static int migrate_folio_move(free_folio_t put_new_folio, unsigned long private,
> if (old_page_state & PAGE_WAS_MAPPED)
> remove_migration_ptes(src, dst, false);
>
> + if (old_page_state & PAGE_WAS_ON_DEFERRED_LIST) {
> + struct deferred_split *ds_queue = get_deferred_split_queue(dst);
> +
> + spin_lock(&ds_queue->split_queue_lock);
> + ds_queue->split_queue_len++;
> + list_add(&dst->_deferred_list, &ds_queue->split_queue);
> + spin_unlock(&ds_queue->split_queue_lock);
> + }
> +
> out_unlock_both:
> folio_unlock(dst);
> set_page_owner_migrate_reason(&dst->page, reason);
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