Date: Mon, 10 Sep 2018 20:54:11 -0400 From: Mark Johnston <markj@freebsd.org> To: Robert <robert.ayrapetyan@gmail.com> Cc: freebsd-hackers@freebsd.org Subject: Re: Sudden grow of memory in "Laundry" state Message-ID: <20180911005411.GF2849@raichu> In-Reply-To: <55b0dd7d-19a3-b566-0602-762b783e8ff3@gmail.com> References: <55b0dd7d-19a3-b566-0602-762b783e8ff3@gmail.com>
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On Mon, Sep 10, 2018 at 11:44:52AM -0700, Robert wrote: > Hi, I have a server with FreeBSD 11.2 and 48 Gigs of RAM where an app > with extensive usage of shared memory (24GB allocation) is running. > > After some random amount of time (usually few days of running), there > happens a sudden increase of "Laundry" memory grow (from zero to 24G in > a few minutes). > > Then slowly it reduces. > > Are described symptoms normal and expected? I've never noticed anything > like that on 11.1. The laundry queue contains dirty inactive pages, which need to be written back to the swap device or a filesystem before they can be reused. When the system is short for free pages, it will scan the inactive queue looking for clean pages, which can be freed cheaply. Dirty pages are moved to the laundry queue. My guess is that the system was running without a page shortage for a long time, and suddenly experienced some memory pressure. This caused lots of pages to move from the inactive queue to the laundry queue. Demand for free pages will then cause pages in the laundry queue to be written back and freed, or requeued if the page was referenced after being placed in the laundry queue. "vmstat -s" and "sysctl vm.stats" output might make things more clear. All this is to say that there's nothing particularly abnormal about what you're observing, though it's not clear what effects this behaviour has on your workload, if any. I can't think of any direct reason this would happen on 11.2 but not 11.1.
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