Messages in this thread | | | Subject | Re: [PATCH] af_unix: limit unix_tot_inflight | From | Eric Dumazet <> | Date | Wed, 24 Nov 2010 16:18:26 +0100 |
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Le mercredi 24 novembre 2010 à 15:44 +0100, Andi Kleen a écrit : > Eric Dumazet <eric.dumazet@gmail.com> writes: > > > > diff --git a/net/unix/garbage.c b/net/unix/garbage.c > > index c8df6fd..40df93d 100644 > > --- a/net/unix/garbage.c > > +++ b/net/unix/garbage.c > > @@ -259,9 +259,16 @@ static void inc_inflight_move_tail(struct unix_sock *u) > > } > > > > static bool gc_in_progress = false; > > +#define UNIX_INFLIGHT_TRIGGER_GC 16000 > > It would be better to define this as a percentage of > lowmem. >
I knew somebody would suggest this ;)
Hmm, why bother ?
Do you think 16000 is too big ? Too small ?
1) What would be the percentage of memory ? 1%, 0.001 % ?
On a 16TB machine, a percentage will still give huge latencies to the poor guy that hit the unix_gc().
With 16000, the max latency I had was 11.5 ms (on an Intel E5540 @2.53GHz), instead of more than 2000 ms
I guess it would make more sense to limit to the size of cpu cache anyway.
2) We currently allocate 4096 bytes (on x86_64) to store one file pointer, or 2048 bytes on x86_32.
But we can store in it up to 255 files.
I posted a patch to shrink this to 32 or 16 bytes. Should we then change the heuristic ?
3) Really who needs more than 16000 inflight unix files ?
(inflight unix files means : af_unix file descriptors that were sent (sendfd()) through af_unix, not yet garbage collected.).
4) If we autotune a limit at boot time as a lowmem percentage, some guys then want a /proc/sys/net/core/max_unix_inflight sysctl , just for completeness. One extra sysctl...
I cant see valid uses but programs designed to stress our stack.
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