'\" t
.\"     Title: write_cache_pages
.\"    Author: [FIXME: author] [see http://docbook.sf.net/el/author]
.\" Generator: DocBook XSL Stylesheets v1.79.1 <http://docbook.sf.net/>
.\"      Date: January 2017
.\"    Manual: Memory Management in Linux
.\"    Source: Kernel Hackers Manual 4.8.15
.\"  Language: English
.\"
.TH "WRITE_CACHE_PAGES" "9" "January 2017" "Kernel Hackers Manual 4\&.8\&." "Memory Management in Linux"
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.SH "NAME"
write_cache_pages \- walk the list of dirty pages of the given address space and write all of them\&.
.SH "SYNOPSIS"
.HP \w'int\ write_cache_pages('u
.BI "int write_cache_pages(struct\ address_space\ *\ " "mapping" ", struct\ writeback_control\ *\ " "wbc" ", writepage_t\ " "writepage" ", void\ *\ " "data" ");"
.SH "ARGUMENTS"
.PP
\fImapping\fR
.RS 4
address space structure to write
.RE
.PP
\fIwbc\fR
.RS 4
subtract the number of written pages from *\fIwbc\fR\->nr_to_write
.RE
.PP
\fIwritepage\fR
.RS 4
function called for each page
.RE
.PP
\fIdata\fR
.RS 4
data passed to writepage function
.RE
.SH "DESCRIPTION"
.PP
If a page is already under I/O,
\fBwrite_cache_pages\fR
skips it, even if it\*(Aqs dirty\&. This is desirable behaviour for memory\-cleaning writeback, but it is INCORRECT for data\-integrity system calls such as
\fBfsync\fR\&.
\fBfsync\fR
and
\fBmsync\fR
need to guarantee that all the data which was dirty at the time the call was made get new I/O started against them\&. If wbc\->sync_mode is WB_SYNC_ALL then we were called for data integrity and we must wait for existing IO to complete\&.
.PP
To avoid livelocks (when other process dirties new pages), we first tag pages which should be written back with TOWRITE tag and only then start writing them\&. For data\-integrity sync we have to be careful so that we do not miss some pages (e\&.g\&., because some other process has cleared TOWRITE tag we set)\&. The rule we follow is that TOWRITE tag can be cleared only by the process clearing the DIRTY tag (and submitting the page for IO)\&.
.SH "COPYRIGHT"
.br