On 12/19/20 2:06 AM, John Hubbard wrote: > On 12/17/20 12:05 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); > > I think once should be enough. There is no counter for page dirtiness, > and this kind of accounting is always tracked in the head page, so there > is no reason to repeatedly call set_page_dirty() from the same > spot. > I think that's what we do even today, considering the Dirty bit is only set on the compound head (regardless of accounting). Even without this patch, IIUC we don't call a second set_page_dirty(head) after the first time we dirty it. So probably there's no optimization to do here, as you say. Joao
