Date: Thu, 3 Apr 2014 15:29:03 +0400 From: Dmitry Sivachenko <trtrmitya@gmail.com> To: John Baldwin <jhb@FreeBSD.org> Cc: freebsd-hackers@freebsd.org, =?utf-8?Q?Trond_Endrest=C3=B8l?= <Trond.Endrestol@fagskolen.gjovik.no> Subject: Re: madvise() vs posix_fadvise() Message-ID: <0AF273E6-CD43-417C-A00C-5B7445090D5B@gmail.com> In-Reply-To: <201403271141.41487.jhb@freebsd.org> References: <D6BD48AF-9522-495D-8D54-37854E53C272@gmail.com> <alpine.BSF.2.00.1403211725140.56113@mail.fig.ol.no> <C5489EF2-34D8-412C-88AC-476120D3F1F4@gmail.com> <201403271141.41487.jhb@freebsd.org>
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On 27 =D0=BC=D0=B0=D1=80=D1=82=D0=B0 2014 =D0=B3., at 19:41, John = Baldwin <jhb@FreeBSD.org> wrote: >>=20 >> I know about mlock(2), it is a bit overkill. >> Can someone please explain the difference between = madvise(MADV_WILLNEED) and=20 > posix_fadvise(POSIX_FADV_WILLNEED)? >=20 > Right now FADV_WILLNEED is a nop. (I have some patches to implement = it for > UFS.) I can't recall off the top of my head if MADV_WILLNEED is also = a nop. > However, if both are fully implemented they should be similar in terms = of > requesting async read-ahead. MADV_WILLNEED might also conceivably > pre-create PTEs while FADV_WILLNEED can be used on a file that isn't > mapped but is accessed via read(2). >=20 Hello and thanks for your reply. Right now I am facing the following problem (stable/10): There is a (home-grown) webserver which mmap's a large amount of data = files (total size is a bit below of RAM, say ~90GB of files with 128GB = of RAM). Server writes access.log (several gigabytes per day). Some of mmaped data files are used frequently, some are used rarely. On = startup, server walks through all of these data files so it's content is = read from disk. After some time of running, I see that rarely used data files are purged = from RAM (access to them leads to long-running disk reads) in favour of = disk cache (at 0:00, when I rotate and gzip log file I see Inactive memory goes = down to the value of log file size). Is there any way to tell VM system not to push mmap'ed regions out of = RAM in favour of disk caches?
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