Date: Tue, 24 Nov 2015 17:10:19 -0800 From: John Baldwin <jhb@freebsd.org> To: freebsd-hackers@freebsd.org Cc: Ian Lepore <ian@freebsd.org>, freebsd-hackers <freebsd-hackers@freebsd.org> Subject: Re: vmstat -m strangeness Message-ID: <1769220.C3nP8qXIrX@ralph.baldwin.cx> In-Reply-To: <1445378386.14127.2.camel@freebsd.org> References: <1445378386.14127.2.camel@freebsd.org>
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On Tuesday, October 20, 2015 03:59:46 PM Ian Lepore wrote: > root@wand:~ # vmstat -m | egrep "busdma|bounce|devbuf|Type" > Type InUse MemUse HighUse Requests Size(s) > devbuf 125 10K - 166 16,32,64,256,512,1024 > busdma 922 116K - 922 128 > bounce 385 775K - 385 32,128 > > How do 385 allocations of 32 or 128 bytes add up to 775K? The > answer... 768K of individual pages each allocated via contigmalloc() do > n't show up in that output. Why is that, and is it something that > should be fixed? Hmm. The output is "correct", it's just that these small allocations have relatively high overhead (PAGE_SIZE - 32 for a 32 byte allocation, etc.). Not sure if there's a way to explain (in vmstat output) why the overhead for certain malloc buckets is so high. Perhaps the vmstat(8) manpage could be expanded to explain what MemUse is and list the contigmalloc() case explicitly as one possible reason for high overhead? -- John Baldwin
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