Re: [PATCH 04/13] mm: Add functions to lock invalidate_lock for two mappings

Damien Le Moal
2021-05-26T12:11:54Z

On 2021/05/26 19:07, Jan Kara wrote:
> On Tue 25-05-21 13:48:05, Darrick J. Wong wrote:
>> On Tue, May 25, 2021 at 03:50:41PM +0200, Jan Kara wrote:
>>> Some operations such as reflinking blocks among files will need to lock
>>> invalidate_lock for two mappings. Add helper functions to do that.
>>>
>>> Signed-off-by: Jan Kara <jack@suse.cz>
>>> ---
>>> include/linux/fs.h | 6 ++++++
>>> mm/filemap.c | 38 ++++++++++++++++++++++++++++++++++++++
>>> 2 files changed, 44 insertions(+)
>>>
>>> diff --git a/include/linux/fs.h b/include/linux/fs.h
>>> index 897238d9f1e0..e6f7447505f5 100644
>>> --- a/include/linux/fs.h
>>> +++ b/include/linux/fs.h
>>> @@ -822,6 +822,12 @@ static inline void inode_lock_shared_nested(struct inode *inode, unsigned subcla
>>> void lock_two_nondirectories(struct inode *, struct inode*);
>>> void unlock_two_nondirectories(struct inode *, struct inode*);
>>>
>>> +void filemap_invalidate_down_write_two(struct address_space *mapping1,
>>> + struct address_space *mapping2);
>>> +void filemap_invalidate_up_write_two(struct address_space *mapping1,
>>
>> TBH I find myself wishing that the invalidate_lock used the same
>> lock/unlock style wrappers that we use for i_rwsem.
>>
>> filemap_invalidate_lock(inode1->mapping);
>> filemap_invalidate_lock_two(inode1->i_mapping, inode2->i_mapping);
>
> OK, and filemap_invalidate_lock_shared() for down_read()? I guess that
> works for me.

What about filemap_invalidate_lock_read() and filemap_invalidate_lock_write() ?
That reminds the down_read()/down_write() without the slightly confusing down/up.

>
> Honza
>
>
>> To be fair, I've never been able to keep straight that down means lock
>> and up means unlock. Ah well, at least you didn't use "p" and "v".
>>
>> Mechanically, the changes look ok to me.
>> Acked-by: Darrick J. Wong <djwong@kernel.org>
>>
>> --D
>>
>>> + struct address_space *mapping2);
>>> +
>>> +
>>> /*
>>> * NOTE: in a 32bit arch with a preemptable kernel and
>>> * an UP compile the i_size_read/write must be atomic
>>> diff --git a/mm/filemap.c b/mm/filemap.c
>>> index 4d9ec4c6cc34..d3801a9739aa 100644
>>> --- a/mm/filemap.c
>>> +++ b/mm/filemap.c
>>> @@ -1009,6 +1009,44 @@ struct page *__page_cache_alloc(gfp_t gfp)
>>> EXPORT_SYMBOL(__page_cache_alloc);
>>> #endif
>>>
>>> +/*
>>> + * filemap_invalidate_down_write_two - lock invalidate_lock for two mappings
>>> + *
>>> + * Lock exclusively invalidate_lock of any passed mapping that is not NULL.
>>> + *
>>> + * @mapping1: the first mapping to lock
>>> + * @mapping2: the second mapping to lock
>>> + */
>>> +void filemap_invalidate_down_write_two(struct address_space *mapping1,
>>> + struct address_space *mapping2)
>>> +{
>>> + if (mapping1 > mapping2)
>>> + swap(mapping1, mapping2);
>>> + if (mapping1)
>>> + down_write(&mapping1->invalidate_lock);
>>> + if (mapping2 && mapping1 != mapping2)
>>> + down_write_nested(&mapping2->invalidate_lock, 1);
>>> +}
>>> +EXPORT_SYMBOL(filemap_invalidate_down_write_two);
>>> +
>>> +/*
>>> + * filemap_invalidate_up_write_two - unlock invalidate_lock for two mappings
>>> + *
>>> + * Unlock exclusive invalidate_lock of any passed mapping that is not NULL.
>>> + *
>>> + * @mapping1: the first mapping to unlock
>>> + * @mapping2: the second mapping to unlock
>>> + */
>>> +void filemap_invalidate_up_write_two(struct address_space *mapping1,
>>> + struct address_space *mapping2)
>>> +{
>>> + if (mapping1)
>>> + up_write(&mapping1->invalidate_lock);
>>> + if (mapping2 && mapping1 != mapping2)
>>> + up_write(&mapping2->invalidate_lock);
>>> +}
>>> +EXPORT_SYMBOL(filemap_invalidate_up_write_two);
>>> +
>>> /*
>>> * In order to wait for pages to become available there must be
>>> * waitqueues associated with pages. By using a hash table of
>>> --
>>> 2.26.2
>>>

--
Damien Le Moal
Western Digital Research