Date: Thu, 20 Aug 2020 14:16:08 +0100 From: Steve O'Hara-Smith <steve@sohara.org> To: Odhiambo Washington <odhiambo@gmail.com> Cc: questions <questions@freebsd.org> Subject: Re: Swapping when memory is idle?? Message-ID: <20200820141608.a8bb35f9dd089d9bc190253b@sohara.org> In-Reply-To: <CAAdA2WP8cr-uRgDRT_GX0faCSAFWORn9UMwqLZOWtLgXd0Hc9w@mail.gmail.com> References: <CAAdA2WP8cr-uRgDRT_GX0faCSAFWORn9UMwqLZOWtLgXd0Hc9w@mail.gmail.com>
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On Thu, 20 Aug 2020 10:53:27 +0300 Odhiambo Washington <odhiambo@gmail.com> wrote: > I have a machine with 16GB RAM and not heavily used. > I see from `top` some things that I do not understand well. > Why would a system use swap when memory is idle? The system will push pages out to swap in response to memory pressure, trying to choose the pages least likely to be used soon. Once the memory pressure recovers there will be free memory again - and the pressure may only last a tiny amount of time. However once a page is pushed out to swap it will stay there until something tries to use it - many processes have quite a lot of memory that is only touched during initialisation and that is a prime candidate for being swapped out ... of course it tends to stay that way. This is of course a good thing because it clears memory of useless cruft so next time there's a bit of memory pressure maybe nothing has to be swapped out. -- Steve O'Hara-Smith <steve@sohara.org>
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