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Top Forums UNIX for Advanced & Expert Users Memory fragmentation in a Linux settop box Post 302917555 by achenle on Wednesday 17th of September 2014 12:44:43 PM
Old 09-17-2014
That depends on how you're doing your IO operations. How are your apps coded to do read and/or stream your files? Do you have control over your application IO? What filesystem(s) are you using for data?

Assuming you're streaming video files without much random searching, you should be using direct IO and bypassing the cache since it's extremely unlikely that the proper file data will be cached when you do any searching.

Direct IO will be faster and it won't fragment memory because you won't be using the page cache.

Caching of file data only helps when data can be held in memory long enough to allow multiple reads of the same data, or when write operations are small and/or slow enough to be effectively coalesced into a smaller number of write operations. Streaming or copying large files fits neither of those criteria.
 

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STREAM(3)						     Library Functions Manual							 STREAM(3)

NAME
stream - a structure for communications SYNOPSIS
bind streamdevice dir dir/data dir/ctl DESCRIPTION
A stream is not a device per se. However, many devices use the streams package in the kernel to implement communications channels. The properties described here are common to all such channels. All streams are represented by two standard files, ctl and data, plus any others the particular device wants to add. Reading and writing the data file receives and sends data on the channel. If the channel is message oriented, each write will represent a message and each read will return at most one message. If the buffer given in a read is smaller than the message, subsequent reads will return the remain- der of the message. Writing textual command strings to the ctl file performs control operations on the stream. The strings need not be null-terminated. Each device may add to the control operations. The common control operations are: hangup Hang up this stream. Any subsequent writes will return an error. The first subsequent read will return 0. All following ones will return an error. push name Push the module name onto the top of the stream. pop Pop the top module off the stream Reading the ctl file returns a textual identifier for the stream. This is used by multiplexed devices and its use is described with the particular device. SEE ALSO
pipe(3), dk(3), cons(3), async(3), fcall(3), ip(3), reboot(3) SOURCE
/sys/src/9/port/st*.c STREAM(3)
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