From 081f211090c3f843f4f3f86cd4549f35b7d5a41a Mon Sep 17 00:00:00 2001 From: Joshua Hahn Date: Tue, 5 Aug 2025 13:50:47 -0700 Subject: [PATCH] mempolicy: clarify what zone reclaim means The zone_reclaim_mode API controls the reclaim behavior when a node runs out of memory. Contrary to its user-facing name, it is internally referred to as "node_reclaim_mode". This can be confusing. But because we cannot change the name of the API since it has been in place since at least 2.6, let's try to be more explicit about what the behavior of this API is. Change the description to clarify what zone reclaim entails, and be explicit about the RECLAIM_ZONE bit, whose purpose has led to some confusion in the past already [1] [2]. While at it, also soften the warning about changing these bits. [1] https://lore.kernel.org/linux-mm/1579005573-58923-1-git-send-email-alex.shi@linux.alibaba.com/ [2] https://lore.kernel.org/linux-mm/20200626003459.D8E015CA@viggo.jf.intel.com/ Link: https://lkml.kernel.org/r/20250805205048.1518453-1-joshua.hahnjy@gmail.com Signed-off-by: Joshua Hahn Acked-by: SeongJae Park Acked-by: David Hildenbrand Reviewed-by: Huang Ying Acked-by: Zi Yan Acked-by: Byungchul Park Cc: Alistair Popple Cc: Byungchul Park Cc: Gregory Price Cc: Mathew Brost Cc: Rakie Kim Signed-off-by: Andrew Morton --- include/uapi/linux/mempolicy.h | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/include/uapi/linux/mempolicy.h b/include/uapi/linux/mempolicy.h index 1f9bb10d1a47..683c130782f0 100644 --- a/include/uapi/linux/mempolicy.h +++ b/include/uapi/linux/mempolicy.h @@ -66,10 +66,16 @@ enum { #define MPOL_F_MORON (1 << 4) /* Migrate On protnone Reference On Node */ /* + * Enabling zone reclaim means the page allocator will attempt to fulfill + * the allocation request on the current node by triggering reclaim and + * trying to shrink the current node. + * Fallback allocations on the next candidates in the zonelist are considered + * when reclaim fails to free up enough memory in the current node/zone. + * * These bit locations are exposed in the vm.zone_reclaim_mode sysctl - * ABI. New bits are OK, but existing bits can never change. + * ABI. New bits are OK, but existing bits should not be changed. */ -#define RECLAIM_ZONE (1<<0) /* Run shrink_inactive_list on the zone */ +#define RECLAIM_ZONE (1<<0) /* Enable zone reclaim */ #define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */ #define RECLAIM_UNMAP (1<<2) /* Unmap pages during reclaim */ -- 2.51.0