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Date: Mon, 13 Aug 2007 16:12:31 +0200 From: Pavel Machek <pavel@....cz> To: Peter Zijlstra <peterz@...radead.org> Cc: Andrew Morton <akpm@...l.org>, kernel list <linux-kernel@...r.kernel.org>, andrea@...e.de, npiggin@...e.de Subject: Re: min_free_kbytes documentation, /proc/sys/vm docs Hi! > > min_free_kbytes documentation says: > > > > min_free_kbytes: > > > > This is used to force the Linux VM to keep a minimum number > > of kilobytes free. The VM uses this number to compute a pages_min > > value for each lowmem zone in the system. Each lowmem zone gets > > a number of reserved free pages based proportionally on its size. > > > > ....which is not too helpful :-(. In particular, should kernel survive > > setting this to 0 and still work reliably? IOW is this > > performance-only tweak, or does it correctness implications? > > correctness > > sort-of, since PF_MEMALLOC usage is currently un-bounded. /me is scared. If this is for correctness... why is it different on different machines? Should we specify some minimum value in the documentation? > > I guess it should also say something like "do not set this to more > > than half of your physical RAM (or half of lowmem?) or you get an > > instant OOM". > > yeah, lowmem, not sure on the oom part, it should work with quite high > limits, although I've never tried it with ridiculous numbers. I did, and it indeed OOMs instantly. Perhaps something like this should be applied? Signed-off-by: Pavel Machek <pavel@...e.cz> diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt 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 Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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