On 2016-02-17 16:17:44 -0500, Rik van Riel wrote: > On Fri, 12 Feb 2016 20:35:53 +0100 > Andres Freund <[email protected]> wrote: > > > On 2016-02-12 13:46:53 +0100, Andres Freund wrote: > > > I'm wondering why pages that are repeatedly written to, in units above > > > the page size, are promoted to the active list? I mean if there never > > > are any reads or re-dirtying an already-dirty page, what's the benefit > > > of moving that page onto the active list? > > > > We chatted about this on IRC and you proposed testing this by removing > > FGP_ACCESSED in grab_cache_page_write_begin. I ran tests with that, > > after removing the aforementioned code to issue posix_fadvise(DONTNEED) > > in postgres. > > That looks promising.
Indeed. > > Here the active/inactive lists didn't change as much as I hoped. A bit > > of reading made it apparent that the workingset logic in > > add_to_page_cache_lru() defated that attempt, > > The patch below should help with that. > > Does the GFP_ACCESSED change still help with the patch > below applied? I've not yet run any tests, but I'd earlier used perf probes to see where pages got activated, and I saw activations from both places. So presumably there'd be a difference; i.e. ISTM we need to change both places. Regards, Andres
