Re: [RFC PATCH v3 15/18] mm: Add balance_dirty_pages_ratelimited_async() function

[Stefan Roesch <shr@fb.com>]

On 5/19/22 1:54 AM, Jan Kara wrote:
> On Thu 19-05-22 01:29:21, Christoph Hellwig wrote:
>>> +static int balance_dirty_pages_ratelimited_flags(struct address_space *mapping,
>>> +						bool no_wait)
>>>  {
>>
>> This doesn't actully take flags, but a single boolean argument.  So
>> either it needs a new name, or we actually pass a descriptiv flag.
>>
>>> +/**
>>> + * balance_dirty_pages_ratelimited_async - balance dirty memory state
>>> + * @mapping: address_space which was dirtied
>>> + *
>>> + * Processes which are dirtying memory should call in here once for each page
>>> + * which was newly dirtied.  The function will periodically check the system's
>>> + * dirty state and will initiate writeback if needed.
>>> + *
>>> + * Once we're over the dirty memory limit we decrease the ratelimiting
>>> + * by a lot, to prevent individual processes from overshooting the limit
>>> + * by (ratelimit_pages) each.
>>> + *
>>> + * This is the async version of the API. It only checks if it is required to
>>> + * balance dirty pages. In case it needs to balance dirty pages, it returns
>>> + * -EAGAIN.
>>> + */
>>> +int  balance_dirty_pages_ratelimited_async(struct address_space *mapping)
>>> +{
>>> +	return balance_dirty_pages_ratelimited_flags(mapping, true);
>>> +}
>>> +EXPORT_SYMBOL(balance_dirty_pages_ratelimited_async);
>>
>> I'd much rather export the underlying
>> balance_dirty_pages_ratelimited_flags helper than adding a pointless
>> wrapper here.  And as long as only iomap is supported there is no need
>> to export it at all.
> 
> This was actually my suggestion so I take the blame ;) I have suggested
> this because I don't like non-static functions with bool arguments (it is
> unnecessarily complicated to understand what the argument means or grep for
> it etc.). If you don't like the wrapper, creating
> 
> int balance_dirty_pages_ratelimited_flags(struct address_space *mapping,
> 					  unsigned int flags)
> 
> and have something like:
> 
> #define BDP_NOWAIT 0x0001
> 

I defined a BDP_ASYNC flag.

> is fine with me as well.
> 
> 								Honza