Mmapped memory goes through the exact same page cache as all other filesystem data -- you probably want to do exactly nothing for optimal performance, the kernel will be smart about what it keeps paged in
On Sat, Feb 6, 2016 at 12:44 PM, Kristoffer Sjögren <[email protected]> wrote: > I'm not looking for fairies :-) I was just curious exactly how mmap > interacts with the OS in order to understand performance metrics > better. > > On Sat, Feb 6, 2016 at 5:46 PM, Howard Chu <[email protected]> wrote: > > Kristoffer Sjögren wrote: > >> > >> Thanks Howard. What's the best documentation on mmap you know, aside > >> from read kernel source code? > > > > > > Not sure what you're asking. Read the mmap(2) manpage and its related > pages. > > If you're thinking there's something fancy hidden in there for you to > take > > advantage of, I don't think you should be using mmap in the first place. > > > > > >> On Fri, Feb 5, 2016 at 10:33 PM, Howard Chu <[email protected]> wrote: > >>> > >>> Kristoffer Sjögren wrote: > >>>> > >>>> > >>>> Hi > >>>> > >>>> Our application do lots of caching using vmtouch, up to a point where > >>>> there isn't a lot of memory left on the machine. We would like to use > >>>> LMDB on the same machine to store around 40GiB data of a few hundred > >>>> million entries. > >>>> > >>>> How can we best understand the interaction and behavior of the OS > >>>> cache and sharing of memory between processes? Is LMDB doing something > >>>> to help the OS? > >>> > >>> > >>> > >>> Nope, LMDB does nothing special with its mmap. > >>> > >>> -- > >>> -- Howard Chu > >>> CTO, Symas Corp. http://www.symas.com > >>> Director, Highland Sun http://highlandsun.com/hyc/ > >>> Chief Architect, OpenLDAP http://www.openldap.org/project/ > >> > >> > > > > > > -- > > -- Howard Chu > > CTO, Symas Corp. http://www.symas.com > > Director, Highland Sun http://highlandsun.com/hyc/ > > Chief Architect, OpenLDAP http://www.openldap.org/project/ > >
