Date: Tue, 11 Oct 2011 12:05:39 +0200 From: Ivan Voras <ivoras@freebsd.org> To: freebsd-hackers@freebsd.org Subject: Re: mmap performance and memory use Message-ID: <j714dj$ggg$1@dough.gmane.org> In-Reply-To: <CAJUyCcMKZ1E5LoJ0BFZju_OH_jjDeqgvBMf8WZ%2BwDvJRFsbH6Q@mail.gmail.com> References: <alpine.BSF.2.00.1110061637270.15552@wojtek.tensor.gdynia.pl> <20111006160159.GQ1511@deviant.kiev.zoral.com.ua> <CAJUyCcMKZ1E5LoJ0BFZju_OH_jjDeqgvBMf8WZ%2BwDvJRFsbH6Q@mail.gmail.com>
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This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enig275D6CCC01AF46E6D4CD92E6 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On 07/10/2011 19:13, Alan Cox wrote: > On Thu, Oct 6, 2011 at 11:01 AM, Kostik Belousov <kostikbel@gmail.com>w= rote: >> For one thing, this indeed causes more memory use for the OS. This is >> somewhat mitigated by automatic use of superpages. Superpage promotion= >> still keeps the 4KB page table around, so most savings from the >> superpages are due to more efficient use of TLB. >> >> > You are correct about the page table page. However, a superpage mappin= g > consumes a single PV entry, in place of 512 or 1024 PV entries. This w= inds > up saving about three physical pages worth of memory for every superpag= e > mapping. But wouldn't the "conservative" superpages policy make it difficult in the OPs case to ever get promotions to superpages if he's touching pages almost randomly? > Similarly, mmap(..., MAP_PREFAULT_READ) on a large, memory resident fil= e may pre-map the file using superpage mappings.=20 grep doesn't find this symbol in the sys src tree in 8-STABLE - nor it seems in /usr/include. But anyway, is there a mechanism which gives more guarantees than "may" (i.e. which forces this) - or if not, how hard would it be to add one? Some Linux-based "enterprise" software (including Java) use Linux-specific calls to allocate large pages directly. --------------enig275D6CCC01AF46E6D4CD92E6 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.18 (FreeBSD) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAk6UFPMACgkQldnAQVacBcjZYgCguCpgO/ThrKRZW83MIhhncDps jkkAn0jcCgePAs5SOlPjJJjvmYkhm9FC =Nxox -----END PGP SIGNATURE----- --------------enig275D6CCC01AF46E6D4CD92E6--
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