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Message-ID: <260C6C62-1BFB-41A0-A433-AD282AF8F23D@nvidia.com>
Date: Mon, 11 Mar 2024 15:56:16 -0400
From: Zi Yan <ziy@...dia.com>
To: Ryan Roberts <ryan.roberts@....com>
Cc: linux-mm@...ck.org, 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>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/migrate: put dest folio on deferred split list if
source was there.
On 11 Mar 2024, at 15:53, Ryan Roberts wrote:
> On 11/03/2024 19:36, 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/
>>
>> 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..84ba1c65d20d 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) &&
>> + !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(src);
>
> do you mean dst here?
Right. I forgot the case of migrating from one node to another and thought
either src or dst works. Thanks.
>
>> +
>> + 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);
--
Best Regards,
Yan, Zi
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