On Wed, 1 Jul 2020, Dave Hansen wrote: > > From: Dave Hansen <[email protected]> > > 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 <[email protected]> > Fixes: 648b5cf368e0 ("mm/vmscan: remove unused RECLAIM_OFF/RECLAIM_ZONE") > Cc: Ben Widawsky <[email protected]> > Cc: Alex Shi <[email protected]> > Cc: Daniel Wagner <[email protected]> > Cc: "Tobin C. Harding" <[email protected]> > Cc: Christoph Lameter <[email protected]> > Cc: Andrew Morton <[email protected]> > Cc: Huang Ying <[email protected]> > Cc: Dan Williams <[email protected]> > Cc: Qian Cai <[email protected]> > Cc: Daniel Wagner <[email protected]> > Cc: [email protected]
Acked-by: David Rientjes <[email protected]>
