Date: Sun, 4 Nov 2012 09:36:13 -0700 From: Warner Losh <imp@bsdimp.com> To: Ian Lepore <freebsd@damnhippie.dyndns.org> Cc: Konstantin Belousov <kostikbel@gmail.com>, freebsd-hackers@freebsd.org, freebsd-embedded@freebsd.org Subject: Re: watchdogd, jemalloc, and mlockall Message-ID: <2D77347F-9913-4727-AA57-204AC266E15C@bsdimp.com> In-Reply-To: <1351968635.1120.110.camel@revolution.hippie.lan> References: <1351967919.1120.102.camel@revolution.hippie.lan> <20121103184143.GC73505@kib.kiev.ua> <1351968635.1120.110.camel@revolution.hippie.lan>
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On Nov 3, 2012, at 12:50 PM, Ian Lepore wrote: > On Sat, 2012-11-03 at 20:41 +0200, Konstantin Belousov wrote: >> On Sat, Nov 03, 2012 at 12:38:39PM -0600, Ian Lepore wrote: >>> In an attempt to un-hijack the thread about memory usage increase >>> between 6.4 and 9.x, I'm starting a new thread here related to my recent >>> discovery that watchdogd uses a lot more memory since it began using >>> mlockall(2). >>> >>> I tried statically linking watchdogd and it made a small difference in >>> RSS, presumably because it doesn't wire down all of libc and libm. >>> >>> VSZ RSS >>> 10236 10164 Dynamic >>> 8624 8636 Static >>> >>> Those numbers are from ps -u on an arm platform. I just updated the PR >>> (bin/173332) with some procstat -v output comparing with/without >>> mlockall(). >>> >>> It appears that the bulk of the new RSS bloat comes from jemalloc >>> allocating vmspace in 8MB chunks. With mlockall(MCL_FUTURE) in effect >>> that leads to wiring 8MB to satisfy what probably amounts to a few >>> hundred bytes of malloc'd memory. >>> >>> It would probably also be a good idea to remove the floating point from >>> watchdogd to avoid wiring all of libm. The floating point is used just >>> to turn the timeout-in-seconds into a power-of-two-nanoseconds value. >>> There's probably a reasonably efficient way to do that without calling >>> log(), considering that it only happens once at program startup. >> >> No, I propose to add a switch to turn on/off the mlockall() call. >> I have no opinion on the default value of the suggested switch. > > In a patch I submitted along with the PR, I added code to query the > vm.swap_enabled sysctl and only call mlockall() when swapping is > enabled. > > Nobody yet has said anything about what seems to me to be the real > problem here: jemalloc grabs 8MB at a time even if you only need to > malloc a few bytes, and there appears to be no way to control that > behavior. Or maybe there's a knob in there that didn't jump out at me > on a quick glance through the header files. Isn't that only for non-production builds? Warner
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