Date: Wed, 30 Jan 2013 13:56:09 -0800 From: Artem Belevich <art@freebsd.org> To: Kevin Day <toasty@dragondata.com> Cc: FreeBSD Filesystems <freebsd-fs@freebsd.org> Subject: Re: Improving ZFS performance for large directories Message-ID: <CAFqOu6gmyQLD5VPOPpyXjWd6quUYh6mvavVbLDP3rLc4kBHbgg@mail.gmail.com> In-Reply-To: <D606CCAE-511F-46DC-838B-E1994B973309@dragondata.com> References: <19DB8F4A-6788-44F6-9A2C-E01DEA01BED9@dragondata.com> <5267B97C-ED47-4AAB-8415-12D6987E9371@gmail.com> <47975CEB-EA50-4F6C-8C47-6F32312F34C4@dragondata.com> <23E6691A-F30C-4731-9F78-FD8ADDDA09AE@gmail.com> <D606CCAE-511F-46DC-838B-E1994B973309@dragondata.com>
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On Wed, Jan 30, 2013 at 12:59 PM, Kevin Day <toasty@dragondata.com> wrote: > > Does anyone here understand the significance of "used" being higher than "limit"? Is the limit only a suggestion, or are there cases where there'a certain metadata that must be in arc, and it's particularly large here? arc_meta_limit is a soft limit which basically tells ARC to attempt evicting metadata entries and reuse their buffers as opposed to allocating new memory and growing ARC. According to the comment next to arc_evict() function, it's a best-effort attempt and eviction is not guaranteed. That could potentially allow meta_size to remain above meta_limit. --Artem
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