vm.txt: document min_free_pages as critical for correctness

[Pavel Machek]

min_free_pages is critical for correctness, document it as such.

Signed-off-by: Pavel Machek <pavel@xxxxxxx>

index a0ccc5b..e460c19 100644
--- a/Documentation/sysctl/vm.txt
+++ b/Documentation/sysctl/vm.txt
@@ -111,6 +111,12 @@ of kilobytes free.  The VM uses this num
 value for each lowmem zone in the system.  Each lowmem zone gets 
 a number of reserved free pages based proportionally on its size.
 
+Some minimal ammount of memory is needed to satisfy PF_MEMALLOC
+allocations; if you set this to lower than 1024KB, your system will
+become subtly broken, and prone to deadlock under high loads.
+
+Setting this too high will OOM your machine instantly.
+
 ==============================================================
 
 percpu_pagelist_fraction


-- 
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