Date: Tue, 11 Oct 2011 12:36:05 -0500 From: Mark Tinguely <marktinguely@gmail.com> To: Alan Cox <alc@rice.edu> Cc: alc@freebsd.org, Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl>, Kostik Belousov <kostikbel@gmail.com>, hackers@freebsd.org, Grzegorz Kulewski <grzegorz@kulewski.pl> Subject: Re: mmap performance and memory use Message-ID: <4E947E85.2040103@gmail.com> In-Reply-To: <4E946AFA.6060105@rice.edu> 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> <alpine.BSF.2.00.1110071916190.8664@wojtek.tensor.gdynia.pl> <4E8FF4B8.7010300@rice.edu> <alpine.BSF.2.00.1110102325220.67653@wojtek.tensor.gdynia.pl> <4E946AFA.6060105@rice.edu>
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On 10/11/2011 11:12 AM, Alan Cox wrote: > On 10/10/2011 16:28, Wojciech Puchar wrote: >> is it possible to force VM subsystem to operate on superpages when >> possible - i mean swapping in 2MB chunks? >> > > Currently, no. For some applications, like the Sun/Oracle JVM, that > have code to explicitly manage large pages, there could be some > benefit in the form of reduced overhead. So, it's on my "to do" list, > but no where near the top of that list. > > Alan > Am I correct in remembering that super-pages have to be aligned on the super-page boundary and be contiguous? If so, in the mmap(), he may want to include the 'MAP_FIXED' flag with an address that is on a super-page boundary. Right now, the "VMFS_ALIGNED_SPACE" that does the VA super-page alignment is only used for device pagers. Similarly, if the allocated physical pages for the object are not contiguous, then MAP_PREFAULT_READ will not result in a super-page promotion. --Mark Tinguely
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