Messages in this thread | | | From | "Huang\, Ying" <> | Subject | Re: [PATCH 1/3] mm/vmscan: restore zone_reclaim_mode ABI | Date | Thu, 02 Jul 2020 19:28:55 +0800 |
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Dave Hansen <dave.hansen@linux.intel.com> writes:
> 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
Per my understanding, this script would have enabled node reclaim for clean unmapped pages before commit 648b5cf368e0 ("mm/vmscan: remove unused RECLAIM_OFF/RECLAIM_ZONE"). So we should revise the description here?
> 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. >
Best Regards, Huang, Ying
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