Date: Tue, 5 May 2020 10:59:01 +0100 From: Steve O'Hara-Smith <steve@sohara.org> To: Nikita Stepanov <nikitastepanov113@yandex.kz> Cc: freebsd-questions@freebsd.org Subject: Re: Does swap increase freebsd performance? Message-ID: <20200505105901.4306c0f7aa0aec652e2cc65a@sohara.org> In-Reply-To: <3971481588671556@myt2-8316c2cade1b.qloud-c.yandex.net> References: <3971481588671556@myt2-8316c2cade1b.qloud-c.yandex.net>
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On Tue, 05 May 2020 15:39:16 +0600 Nikita Stepanov <nikitastepanov113@yandex.kz> wrote: We seem to be getting a rash of bodyless messages with the question in the subject. Please type a body with your question even if it is a repeat of the subject. Swap can increase performance by making more of the memory available for active use. Many programs have memory allocated that is very rarely used or even only used at startup, pushing this out to swap frees physical memory for more active use such as caching. Whether this makes a difference to performance or not depends greatly on the workload, or more importantly the memory pressure the workload produces. If there is plenty of memory then swap won't help and there is overhead involved in writing pages out to swap so it will reduce performance very slightly. If there is just about enough memory then swap will make it more useful and increase performance. This 'sweet spot' is in reality often quite wide depending on the benefits of caching on workload and so forth. If there is insufficient memory then swap will keep things working but performance will suffer badly. This can be very important in the face of an unusual load spike. -- Steve O'Hara-Smith <steve@sohara.org>
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