'\" t .\" Title: set_dma_reserve .\" Author: [FIXME: author] [see http://docbook.sf.net/el/author] .\" Generator: DocBook XSL Stylesheets v1.79.1 .\" Date: April 2019 .\" Manual: Memory Management in Linux .\" Source: Kernel Hackers Manual 4.9.168 .\" Language: English .\" .TH "SET_DMA_RESERVE" "9" "April 2019" "Kernel Hackers Manual 4\&.9\&." "Memory Management in Linux" .\" ----------------------------------------------------------------- .\" * Define some portability stuff .\" ----------------------------------------------------------------- .\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .\" http://bugs.debian.org/507673 .\" http://lists.gnu.org/archive/html/groff/2009-02/msg00013.html .\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .ie \n(.g .ds Aq \(aq .el .ds Aq ' .\" ----------------------------------------------------------------- .\" * set default formatting .\" ----------------------------------------------------------------- .\" disable hyphenation .nh .\" disable justification (adjust text to left margin only) .ad l .\" ----------------------------------------------------------------- .\" * MAIN CONTENT STARTS HERE * .\" ----------------------------------------------------------------- .SH "NAME" set_dma_reserve \- set the specified number of pages reserved in the first zone .SH "SYNOPSIS" .HP \w'void\ set_dma_reserve('u .BI "void set_dma_reserve(unsigned\ long\ " "new_dma_reserve" ");" .SH "ARGUMENTS" .PP \fInew_dma_reserve\fR .RS 4 The number of pages to mark reserved .RE .SH "DESCRIPTION" .PP The per\-cpu batchsize and zone watermarks are determined by managed_pages\&. In the DMA zone, a significant percentage may be consumed by kernel image and other unfreeable allocations which can skew the watermarks badly\&. This function may optionally be used to account for unfreeable pages in the first zone (e\&.g\&., ZONE_DMA)\&. The effect will be lower watermarks and smaller per\-cpu batchsize\&. .SH "COPYRIGHT" .br