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Date: Thu, 31 Jan 2008 17:05:36 -0800 (PST) From: David Miller <davem@...emloft.net> To: dada1@...mosbay.com Cc: netdev@...r.kernel.org, Robert.Olsson@...a.slu.se Subject: Re: [IPV4] route cache: Introduce rt_genid for smooth cache invalidation From: Eric Dumazet <dada1@...mosbay.com> Date: Wed, 30 Jan 2008 09:08:56 +0100 > Current ip route cache implementation is not suited to large caches. > > We can consume a lot of CPU when cache must be invalidated, since we > currently need to evict all cache entries, and this eviction is > sometimes asynchronous. min_delay & max_delay can somewhat control this > asynchronism behavior, but whole thing is a kludge, regularly triggering > infamous soft lockup messages. When entries are still in use, this also > consumes a lot of ram, filling dst_garbage.list. > > A better scheme is to use a generation identifier on each entry, > so that cache invalidation can be performed by changing the table > identifier, without having to scan all entries. > No more delayed flushing, no more stalling when secret_interval expires. > > Invalidated entries will then be freed at GC time (controled by > ip_rt_gc_timeout or stress), or when an invalidated entry is found > in a chain when an insert is done. > Thus we keep a normal equilibrium. > > This patch : > - renames rt_hash_rnd to rt_genid (and makes it an atomic_t) > - Adds a new rt_genid field to 'struct rtable' (filling a hole on 64bit) > - Checks entry->rt_genid at appropriate places : > --- Readers have to ignore invalidated entries. > --- Writers can delete invalidated entries. > - Removes rt_flush_timer timer > - Removes unused /proc/sys/net/ipv4/{min_delay,max_delay} > > We even reduce size of route.o > > # size net/ipv4/route.o > text data bss dec hex filename > 20038 1331 160 21529 5419 net/ipv4/route.o.before > 19991 1203 104 21298 5332 net/ipv4/route.o > > Next step will be to audit all rt_cache_flush(0) (aka flushes) users, see > if they can be converted to "invalidate the cache" users. > > Signed-off-by: Eric Dumazet <dada1@...mosbay.com> This looks really nice, applied, thanks Eric. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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