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SubjectRe: [PATCH 5/8] migrate_pages: batch _unmap and _move
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Andrew Morton <akpm@linux-foundation.org> writes:

> On Tue, 27 Dec 2022 08:28:56 +0800 Huang Ying <ying.huang@intel.com> wrote:
>
>> In this patch the _unmap and _move stage of the folio migration is
>> batched. That for, previously, it is,
>>
>> for each folio
>> _unmap()
>> _move()
>>
>> Now, it is,
>>
>> for each folio
>> _unmap()
>> for each folio
>> _move()
>>
>> Based on this, we can batch the TLB flushing and use some hardware
>> accelerator to copy folios between batched _unmap and batched _move
>> stages.
>>
>> ...
>>
>> --- a/mm/migrate.c
>> +++ b/mm/migrate.c
>> @@ -1027,8 +1027,32 @@ static void __migrate_folio_extract(struct folio *dst,
>> dst->private = NULL;
>> }
>>
>> +static void migrate_folio_undo_src(struct folio *src,
>> + int page_was_mapped,
>> + struct anon_vma *anon_vma,
>> + struct list_head *ret)
>> +{
>> + if (page_was_mapped)
>> + remove_migration_ptes(src, src, false);
>> + if (anon_vma)
>> + put_anon_vma(anon_vma);
>> + folio_unlock(src);
>> + list_move_tail(&src->lru, ret);
>> +}
>> +
>> +static void migrate_folio_undo_dst(struct folio *dst,
>> + free_page_t put_new_page,
>> + unsigned long private)
>> +{
>> + folio_unlock(dst);
>> + if (put_new_page)
>> + put_new_page(&dst->page, private);
>> + else
>> + folio_put(dst);
>> +}
>
> What do the above do? Are they so obvious that no comments are needed?

Thank you for reminding, will add comments.

>
>> static int __migrate_folio_unmap(struct folio *src, struct folio *dst,
>> - int force, enum migrate_mode mode)
>> + int force, bool force_lock, enum migrate_mode mode)
>> {
>> int rc = -EAGAIN;
>> int page_was_mapped = 0;
>> @@ -1055,6 +1079,11 @@ static int __migrate_folio_unmap(struct folio *src, struct folio *dst,
>> if (current->flags & PF_MEMALLOC)
>> goto out;
>>
>> + if (!force_lock) {
>> + rc = -EDEADLOCK;
>> + goto out;
>> + }
>
> Please document the use of EDEADLOCK in this code. What does it signify?

Sure. Will do that in the next version.

Best Regards,
Huang, Ying

>> folio_lock(src);
>> }
>>

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