Re: [PATCH RFC 7/9] mm/gup: Decrement head page once for group of subpages

[Joao Martins <joao.m.martins@oracle.com>]

On 12/17/20 8:05 PM, Jason Gunthorpe wrote:
> On Thu, Dec 17, 2020 at 07:05:37PM +0000, Joao Martins wrote:
>>> No reason not to fix set_page_dirty_lock() too while you are here.
>>
>> The wack of atomics you mentioned earlier you referred to, I suppose it
>> ends being account_page_dirtied(). See partial diff at the end.
> 
> Well, even just eliminating the lock_page, page_mapping, PageDirty,
> etc is already a big win.
> 
> If mapping->a_ops->set_page_dirty() needs to be called multiple times
> on the head page I'd probably just suggest:
> 
>   while (ntails--)
>         rc |= (*spd)(head);
> 
> At least as a start.
> 
/me nods

> If you have workloads that have page_mapping != NULL then look at
> another series to optimze that. Looks a bit large though given the
> number of places implementing set_page_dirty
> 
Yes. I don't have a particular workload, was just wondering what you had in
mind, as at a glance, changing all the places without messing filesystems looks like
the subject of a separate series.

> I think the current reality is calling set_page_dirty on an actual
> file system is busted anyhow, so I think mapping is generally going to
> be NULL here?

Perhaps -- I'll have to check.

	Joao
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