(split) LDP: Update original to LDP v3.65

[linuxjm/LDP_man-pages.git] / original / man2 / readahead.2

diff --git a/original/man2/readahead.2 b/original/man2/readahead.2
index 08c2fe2..9605d50 100644 (file)
--- a/original/man2/readahead.2
+++ b/original/man2/readahead.2
@@ -25,9 +25,9 @@
 .\" 2004-05-40 Created by Michael Kerrisk <mtk.manpages@gmail.com>
 .\" 2004-10-05 aeb, minor correction
 .\"
-.TH READAHEAD 2 2010-09-10 "Linux" "Linux Programmer's Manual"
+.TH READAHEAD 2 2014-03-15 "Linux" "Linux Programmer's Manual"
 .SH NAME
-readahead \- perform file readahead into page cache
+readahead \- initiate file readahead into page cache
 .SH SYNOPSIS
 .nf
 .BR "#define _GNU_SOURCE" "             /* See feature_test_macros(7) */"
@@ -37,8 +37,11 @@ readahead \- perform file readahead into page cache
 .fi
 .SH DESCRIPTION
 .BR readahead ()
-populates the page cache with data from a file so that subsequent
-reads from that file will not block on disk I/O.
+initiates readahead on a file so that subsequent reads from that file will
+be satisfied from the cache, and not block on disk I/O
+(assuming the readahead was initiated early enough and that other activity
+on the system did not in the meantime flush pages from the cache).
+
 The
 .I fd
 argument is a file descriptor identifying the file which is
@@ -57,8 +60,6 @@ equal to
 .IR "(offset+count)" .
 .BR readahead ()
 does not read beyond the end of the file.
-.BR readahead ()
-blocks until the specified data has been read.
 The current file offset of the open file referred to by
 .I fd
 is left unchanged.
@@ -89,9 +90,31 @@ The
 .BR readahead ()
 system call is Linux-specific, and its use should be avoided
 in portable applications.
+.SH NOTES
+On some 32-bit architectures,
+the calling signature for this system call differs,
+for the reasons described in
+.BR syscall (2).
+.SH BUGS
+.BR readahead ()
+attempts to schedule the reads in the background and return immediately.
+However, it may block while it reads the filesystem metadata needed
+to locate the requested blocks.
+This occurs frequently with ext[234] on large files
+using indirect blocks instead of extents,
+giving the appearance that the call blocks until the requested data has
+been read.
 .SH SEE ALSO
 .BR lseek (2),
 .BR madvise (2),
 .BR mmap (2),
 .BR posix_fadvise (2),
 .BR read (2)
+.SH COLOPHON
+This page is part of release 3.65 of the Linux
+.I man-pages
+project.
+A description of the project,
+and information about reporting bugs,
+can be found at
+\%http://www.kernel.org/doc/man\-pages/.