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SubjectRe: [PATCH]: 1/4 batch mark_page_accessed()

<snip>

> > > On the other hand, without batching you mix the locality up in LRU - the LRU becomes
> > > more precise in terms of "LRU aging", but less ordered in terms of sequential
> > > access pattern.
> > >
> > > The disk IO intensive reaim has very significant gain from the batching, its
> > > probably due to the enhanced LRU ordering (what Nikita says).
> > >
> > > The slowdown is probably due to the additional atomic_inc by page_cache_get().
> > >
> > > Is there no way to avoid such page_cache_get there (and in lru_cache_add also)?
> >
> > Not really. The page is only in the pagevec at that time - if someone does
> > a put_page() on it the page will be freed for real, and will then be
> > spilled onto the LRU. Messy.
>
> I don't think that atomic_inc will be particularly
> costly. generic_file_{write,read}() call find_get_page() just before
> calling mark_page_accessed(), so cache-line with page reference counter
> is most likely still exclusive owned by this CPU.

Assuming that is true - what could cause the slowdown?

There are only benefits from the makr_page_accessed batching, I can't
see any drawbacks. Do you?
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