Messages in this thread | | | Date | Wed, 1 Jul 2020 13:03:20 -0700 (PDT) | From | David Rientjes <> | Subject | Re: [PATCH 1/3] mm/vmscan: restore zone_reclaim_mode ABI |
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On Wed, 1 Jul 2020, Dave Hansen wrote:
> > From: Dave Hansen <dave.hansen@linux.intel.com> > > I went to go add a new RECLAIM_* mode for the zone_reclaim_mode > sysctl. Like a good kernel developer, I also went to go update the > documentation. I noticed that the bits in the documentation didn't > match the bits in the #defines. > > The VM never explicitly checks the RECLAIM_ZONE bit. The bit is, > however implicitly checked when checking 'node_reclaim_mode==0'. > The RECLAIM_ZONE #define was removed in a cleanup. That, by itself > is fine. > > But, when the bit was removed (bit 0) the _other_ bit locations also > got changed. That's not OK because the bit values are documented to > mean one specific thing and users surely rely on them meaning that one > thing and not changing from kernel to kernel. The end result is that > if someone had a script that did: > > sysctl vm.zone_reclaim_mode=1 > > That script went from doing nothing to writing out pages during > node reclaim after the commit in question. That's not great. > > Put the bits back the way they were and add a comment so something > like this is a bit harder to do again. Update the documentation to > make it clear that the first bit is ignored. > > Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> > Fixes: 648b5cf368e0 ("mm/vmscan: remove unused RECLAIM_OFF/RECLAIM_ZONE") > Cc: Ben Widawsky <ben.widawsky@intel.com> > Cc: Alex Shi <alex.shi@linux.alibaba.com> > Cc: Daniel Wagner <dwagner@suse.de> > Cc: "Tobin C. Harding" <tobin@kernel.org> > Cc: Christoph Lameter <cl@linux.com> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Huang Ying <ying.huang@intel.com> > Cc: Dan Williams <dan.j.williams@intel.com> > Cc: Qian Cai <cai@lca.pw> > Cc: Daniel Wagner <dwagner@suse.de> > Cc: stable@vger.kernel.org
Acked-by: David Rientjes <rientjes@google.com>
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