Revision 0ee931c4e31a5efb134c76440405e9219f896e33 authored by Michal Hocko on 13 September 2017, 23:28:29 UTC, committed by Linus Torvalds on 14 September 2017, 01:53:16 UTC
GFP_TEMPORARY was introduced by commit e12ba74d8ff3 ("Group short-lived and reclaimable kernel allocations") along with __GFP_RECLAIMABLE. It's primary motivation was to allow users to tell that an allocation is short lived and so the allocator can try to place such allocations close together and prevent long term fragmentation. As much as this sounds like a reasonable semantic it becomes much less clear when to use the highlevel GFP_TEMPORARY allocation flag. How long is temporary? Can the context holding that memory sleep? Can it take locks? It seems there is no good answer for those questions. The current implementation of GFP_TEMPORARY is basically GFP_KERNEL | __GFP_RECLAIMABLE which in itself is tricky because basically none of the existing caller provide a way to reclaim the allocated memory. So this is rather misleading and hard to evaluate for any benefits. I have checked some random users and none of them has added the flag with a specific justification. I suspect most of them just copied from other existing users and others just thought it might be a good idea to use without any measuring. This suggests that GFP_TEMPORARY just motivates for cargo cult usage without any reasoning. I believe that our gfp flags are quite complex already and especially those with highlevel semantic should be clearly defined to prevent from confusion and abuse. Therefore I propose dropping GFP_TEMPORARY and replace all existing users to simply use GFP_KERNEL. Please note that SLAB users with shrinkers will still get __GFP_RECLAIMABLE heuristic and so they will be placed properly for memory fragmentation prevention. I can see reasons we might want some gfp flag to reflect shorterm allocations but I propose starting from a clear semantic definition and only then add users with proper justification. This was been brought up before LSF this year by Matthew [1] and it turned out that GFP_TEMPORARY really doesn't have a clear semantic. It seems to be a heuristic without any measured advantage for most (if not all) its current users. The follow up discussion has revealed that opinions on what might be temporary allocation differ a lot between developers. So rather than trying to tweak existing users into a semantic which they haven't expected I propose to simply remove the flag and start from scratch if we really need a semantic for short term allocations. [1] http://lkml.kernel.org/r/20170118054945.GD18349@bombadil.infradead.org [akpm@linux-foundation.org: fix typo] [akpm@linux-foundation.org: coding-style fixes] [sfr@canb.auug.org.au: drm/i915: fix up] Link: http://lkml.kernel.org/r/20170816144703.378d4f4d@canb.auug.org.au Link: http://lkml.kernel.org/r/20170728091904.14627-1-mhocko@kernel.org Signed-off-by: Michal Hocko <mhocko@suse.com> Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au> Acked-by: Mel Gorman <mgorman@suse.de> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Matthew Wilcox <willy@infradead.org> Cc: Neil Brown <neilb@suse.de> Cc: "Theodore Ts'o" <tytso@mit.edu> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 parent d0dbf77
merge_config.sh
#!/bin/sh
# merge_config.sh - Takes a list of config fragment values, and merges
# them one by one. Provides warnings on overridden values, and specified
# values that did not make it to the resulting .config file (due to missed
# dependencies or config symbol removal).
#
# Portions reused from kconf_check and generate_cfg:
# http://git.yoctoproject.org/cgit/cgit.cgi/yocto-kernel-tools/tree/tools/kconf_check
# http://git.yoctoproject.org/cgit/cgit.cgi/yocto-kernel-tools/tree/tools/generate_cfg
#
# Copyright (c) 2009-2010 Wind River Systems, Inc.
# Copyright 2011 Linaro
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License version 2 as
# published by the Free Software Foundation.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
# See the GNU General Public License for more details.
clean_up() {
rm -f $TMP_FILE
exit
}
trap clean_up HUP INT TERM
usage() {
echo "Usage: $0 [OPTIONS] [CONFIG [...]]"
echo " -h display this help text"
echo " -m only merge the fragments, do not execute the make command"
echo " -n use allnoconfig instead of alldefconfig"
echo " -r list redundant entries when merging fragments"
echo " -O dir to put generated output files. Consider setting \$KCONFIG_CONFIG instead."
}
RUNMAKE=true
ALLTARGET=alldefconfig
WARNREDUN=false
OUTPUT=.
while true; do
case $1 in
"-n")
ALLTARGET=allnoconfig
shift
continue
;;
"-m")
RUNMAKE=false
shift
continue
;;
"-h")
usage
exit
;;
"-r")
WARNREDUN=true
shift
continue
;;
"-O")
if [ -d $2 ];then
OUTPUT=$(echo $2 | sed 's/\/*$//')
else
echo "output directory $2 does not exist" 1>&2
exit 1
fi
shift 2
continue
;;
*)
break
;;
esac
done
if [ "$#" -lt 1 ] ; then
usage
exit
fi
if [ -z "$KCONFIG_CONFIG" ]; then
if [ "$OUTPUT" != . ]; then
KCONFIG_CONFIG=$(readlink -m -- "$OUTPUT/.config")
else
KCONFIG_CONFIG=.config
fi
fi
INITFILE=$1
shift;
if [ ! -r "$INITFILE" ]; then
echo "The base file '$INITFILE' does not exist. Exit." >&2
exit 1
fi
MERGE_LIST=$*
SED_CONFIG_EXP="s/^\(# \)\{0,1\}\(CONFIG_[a-zA-Z0-9_]*\)[= ].*/\2/p"
TMP_FILE=$(mktemp ./.tmp.config.XXXXXXXXXX)
echo "Using $INITFILE as base"
cat $INITFILE > $TMP_FILE
# Merge files, printing warnings on overridden values
for MERGE_FILE in $MERGE_LIST ; do
echo "Merging $MERGE_FILE"
if [ ! -r "$MERGE_FILE" ]; then
echo "The merge file '$MERGE_FILE' does not exist. Exit." >&2
exit 1
fi
CFG_LIST=$(sed -n "$SED_CONFIG_EXP" $MERGE_FILE)
for CFG in $CFG_LIST ; do
grep -q -w $CFG $TMP_FILE || continue
PREV_VAL=$(grep -w $CFG $TMP_FILE)
NEW_VAL=$(grep -w $CFG $MERGE_FILE)
if [ "x$PREV_VAL" != "x$NEW_VAL" ] ; then
echo Value of $CFG is redefined by fragment $MERGE_FILE:
echo Previous value: $PREV_VAL
echo New value: $NEW_VAL
echo
elif [ "$WARNREDUN" = "true" ]; then
echo Value of $CFG is redundant by fragment $MERGE_FILE:
fi
sed -i "/$CFG[ =]/d" $TMP_FILE
done
cat $MERGE_FILE >> $TMP_FILE
done
if [ "$RUNMAKE" = "false" ]; then
cp -T -- "$TMP_FILE" "$KCONFIG_CONFIG"
echo "#"
echo "# merged configuration written to $KCONFIG_CONFIG (needs make)"
echo "#"
clean_up
exit
fi
# If we have an output dir, setup the O= argument, otherwise leave
# it blank, since O=. will create an unnecessary ./source softlink
OUTPUT_ARG=""
if [ "$OUTPUT" != "." ] ; then
OUTPUT_ARG="O=$OUTPUT"
fi
# Use the merged file as the starting point for:
# alldefconfig: Fills in any missing symbols with Kconfig default
# allnoconfig: Fills in any missing symbols with # CONFIG_* is not set
make KCONFIG_ALLCONFIG=$TMP_FILE $OUTPUT_ARG $ALLTARGET
# Check all specified config values took (might have missed-dependency issues)
for CFG in $(sed -n "$SED_CONFIG_EXP" $TMP_FILE); do
REQUESTED_VAL=$(grep -w -e "$CFG" $TMP_FILE)
ACTUAL_VAL=$(grep -w -e "$CFG" "$KCONFIG_CONFIG")
if [ "x$REQUESTED_VAL" != "x$ACTUAL_VAL" ] ; then
echo "Value requested for $CFG not in final .config"
echo "Requested value: $REQUESTED_VAL"
echo "Actual value: $ACTUAL_VAL"
echo ""
fi
done
clean_up
![swh spinner](/static/img/swh-spinner.gif)
Computing file changes ...