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>
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faddr2line
#!/bin/bash
#
# Translate stack dump function offsets.
#
# addr2line doesn't work with KASLR addresses. This works similarly to
# addr2line, but instead takes the 'func+0x123' format as input:
#
# $ ./scripts/faddr2line ~/k/vmlinux meminfo_proc_show+0x5/0x568
# meminfo_proc_show+0x5/0x568:
# meminfo_proc_show at fs/proc/meminfo.c:27
#
# If the address is part of an inlined function, the full inline call chain is
# printed:
#
# $ ./scripts/faddr2line ~/k/vmlinux native_write_msr+0x6/0x27
# native_write_msr+0x6/0x27:
# arch_static_branch at arch/x86/include/asm/msr.h:121
# (inlined by) static_key_false at include/linux/jump_label.h:125
# (inlined by) native_write_msr at arch/x86/include/asm/msr.h:125
#
# The function size after the '/' in the input is optional, but recommended.
# It's used to help disambiguate any duplicate symbol names, which can occur
# rarely. If the size is omitted for a duplicate symbol then it's possible for
# multiple code sites to be printed:
#
# $ ./scripts/faddr2line ~/k/vmlinux raw_ioctl+0x5
# raw_ioctl+0x5/0x20:
# raw_ioctl at drivers/char/raw.c:122
#
# raw_ioctl+0x5/0xb1:
# raw_ioctl at net/ipv4/raw.c:876
#
# Multiple addresses can be specified on a single command line:
#
# $ ./scripts/faddr2line ~/k/vmlinux type_show+0x10/45 free_reserved_area+0x90
# type_show+0x10/0x2d:
# type_show at drivers/video/backlight/backlight.c:213
#
# free_reserved_area+0x90/0x123:
# free_reserved_area at mm/page_alloc.c:6429 (discriminator 2)
set -o errexit
set -o nounset
command -v awk >/dev/null 2>&1 || die "awk isn't installed"
command -v readelf >/dev/null 2>&1 || die "readelf isn't installed"
command -v addr2line >/dev/null 2>&1 || die "addr2line isn't installed"
usage() {
echo "usage: faddr2line <object file> <func+offset> <func+offset>..." >&2
exit 1
}
warn() {
echo "$1" >&2
}
die() {
echo "ERROR: $1" >&2
exit 1
}
# Try to figure out the source directory prefix so we can remove it from the
# addr2line output. HACK ALERT: This assumes that start_kernel() is in
# kernel/init.c! This only works for vmlinux. Otherwise it falls back to
# printing the absolute path.
find_dir_prefix() {
local objfile=$1
local start_kernel_addr=$(readelf -sW $objfile | awk '$8 == "start_kernel" {printf "0x%s", $2}')
[[ -z $start_kernel_addr ]] && return
local file_line=$(addr2line -e $objfile $start_kernel_addr)
[[ -z $file_line ]] && return
local prefix=${file_line%init/main.c:*}
if [[ -z $prefix ]] || [[ $prefix = $file_line ]]; then
return
fi
DIR_PREFIX=$prefix
return 0
}
__faddr2line() {
local objfile=$1
local func_addr=$2
local dir_prefix=$3
local print_warnings=$4
local func=${func_addr%+*}
local offset=${func_addr#*+}
offset=${offset%/*}
local size=
[[ $func_addr =~ "/" ]] && size=${func_addr#*/}
if [[ -z $func ]] || [[ -z $offset ]] || [[ $func = $func_addr ]]; then
warn "bad func+offset $func_addr"
DONE=1
return
fi
# Go through each of the object's symbols which match the func name.
# In rare cases there might be duplicates.
while read symbol; do
local fields=($symbol)
local sym_base=0x${fields[0]}
local sym_type=${fields[1]}
local sym_end=0x${fields[3]}
# calculate the size
local sym_size=$(($sym_end - $sym_base))
if [[ -z $sym_size ]] || [[ $sym_size -le 0 ]]; then
warn "bad symbol size: base: $sym_base end: $sym_end"
DONE=1
return
fi
sym_size=0x$(printf %x $sym_size)
# calculate the address
local addr=$(($sym_base + $offset))
if [[ -z $addr ]] || [[ $addr = 0 ]]; then
warn "bad address: $sym_base + $offset"
DONE=1
return
fi
addr=0x$(printf %x $addr)
# weed out non-function symbols
if [[ $sym_type != t ]] && [[ $sym_type != T ]]; then
[[ $print_warnings = 1 ]] &&
echo "skipping $func address at $addr due to non-function symbol of type '$sym_type'"
continue
fi
# if the user provided a size, make sure it matches the symbol's size
if [[ -n $size ]] && [[ $size -ne $sym_size ]]; then
[[ $print_warnings = 1 ]] &&
echo "skipping $func address at $addr due to size mismatch ($size != $sym_size)"
continue;
fi
# make sure the provided offset is within the symbol's range
if [[ $offset -gt $sym_size ]]; then
[[ $print_warnings = 1 ]] &&
echo "skipping $func address at $addr due to size mismatch ($offset > $sym_size)"
continue
fi
# separate multiple entries with a blank line
[[ $FIRST = 0 ]] && echo
FIRST=0
# pass real address to addr2line
echo "$func+$offset/$sym_size:"
addr2line -fpie $objfile $addr | sed "s; $dir_prefix\(\./\)*; ;"
DONE=1
done < <(nm -n $objfile | awk -v fn=$func '$3 == fn { found=1; line=$0; start=$1; next } found == 1 { found=0; print line, $1 }')
}
[[ $# -lt 2 ]] && usage
objfile=$1
[[ ! -f $objfile ]] && die "can't find objfile $objfile"
shift
DIR_PREFIX=supercalifragilisticexpialidocious
find_dir_prefix $objfile
FIRST=1
while [[ $# -gt 0 ]]; do
func_addr=$1
shift
# print any matches found
DONE=0
__faddr2line $objfile $func_addr $DIR_PREFIX 0
# if no match was found, print warnings
if [[ $DONE = 0 ]]; then
__faddr2line $objfile $func_addr $DIR_PREFIX 1
warn "no match for $func_addr"
fi
done
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