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SubjectRe: [PATCH 2/3] Properly account for the number of page cache pages zone_reclaim() can reclaim
> > > The ideal would be that the number of tmpfs pages would also be known
> > > and account for like NR_FILE_MAPPED as swap is required to discard them.
> > > A means of working this out quickly was not obvious but a comment is added
> > > noting the problem.
> >
> > I'd rather prefer it be accounted separately than to muck up NR_FILE_MAPPED :)
> >
> Maybe I used a poor choice of words. What I meant was that the ideal would
> be we had a separate count for tmpfs pages. As tmpfs pages and mapped pages
> both have to be unmapped and potentially, they are "like" each other with
> respect to the zone_reclaim_mode and how it behaves. We would end up
> with something like
> pagecache_reclaimable -= zone_page_state(zone, NR_FILE_MAPPED);
> pagecache_reclaimable -= zone_page_state(zone, NR_FILE_TMPFS);

Please see shmem_writepage(). tmpfs writeout make swapcache, We also
need to concern swapcache.

note: swapcache also increase NR_FILE_PAGES, see add_to_swap_cache.

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