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Wed, 01 Jul 2020 13:03:02 -0700 (PDT) Date: Wed, 1 Jul 2020 13:03:01 -0700 (PDT) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Dave Hansen cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, ben.widawsky@intel.com, alex.shi@linux.alibaba.com, dwagner@suse.de, tobin@kernel.org, cl@linux.com, akpm@linux-foundation.org, ying.huang@intel.com, dan.j.williams@intel.com, cai@lca.pw Subject: Re: [PATCH 3/3] mm/vmscan: replace implicit RECLAIM_ZONE checks with explicit checks In-Reply-To: <20200701152627.8761147E@viggo.jf.intel.com> Message-ID: References: <20200701152621.D520E62B@viggo.jf.intel.com> <20200701152627.8761147E@viggo.jf.intel.com> User-Agent: Alpine 2.23 (DEB 453 2020-06-18) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Queue-Id: B5652180F8B81 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam01 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, 1 Jul 2020, Dave Hansen wrote: > diff -puN include/linux/swap.h~mm-vmscan-node_reclaim_mode_helper include/linux/swap.h > --- a/include/linux/swap.h~mm-vmscan-node_reclaim_mode_helper 2020-07-01 08:22:13.650955330 -0700 > +++ b/include/linux/swap.h 2020-07-01 08:22:13.659955330 -0700 > @@ -12,6 +12,7 @@ > #include > #include > #include > +#include > #include > > struct notifier_block; > @@ -374,6 +375,12 @@ extern int sysctl_min_slab_ratio; > #define node_reclaim_mode 0 > #endif > > +static inline bool node_reclaim_enabled(void) > +{ > + /* Is any node_reclaim_mode bit set? */ > + return node_reclaim_mode & (RECLAIM_ZONE|RECLAIM_WRITE|RECLAIM_UNMAP); > +} > + > extern void check_move_unevictable_pages(struct pagevec *pvec); > > extern int kswapd_run(int nid); If a user writes a bit that isn't a RECLAIM_* bit to vm.zone_reclaim_mode today, it acts as though RECLAIM_ZONE is enabled: we try to reclaim in zonelist order before falling back to the next zone in the page allocator. The sysctl doesn't enforce any max value :/ I dont know if there is any such user, but this would break them if there is. Should this simply be return !!node_reclaim_mode?