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
lkc_proto.h
#include <stdarg.h>
/* confdata.c */
void conf_parse(const char *name);
int conf_read(const char *name);
int conf_read_simple(const char *name, int);
int conf_write_defconfig(const char *name);
int conf_write(const char *name);
int conf_write_autoconf(void);
bool conf_get_changed(void);
void conf_set_changed_callback(void (*fn)(void));
void conf_set_message_callback(void (*fn)(const char *fmt, va_list ap));
/* menu.c */
extern struct menu rootmenu;
bool menu_is_empty(struct menu *menu);
bool menu_is_visible(struct menu *menu);
bool menu_has_prompt(struct menu *menu);
const char * menu_get_prompt(struct menu *menu);
struct menu * menu_get_root_menu(struct menu *menu);
struct menu * menu_get_parent_menu(struct menu *menu);
bool menu_has_help(struct menu *menu);
const char * menu_get_help(struct menu *menu);
struct gstr get_relations_str(struct symbol **sym_arr, struct list_head *head);
void menu_get_ext_help(struct menu *menu, struct gstr *help);
/* symbol.c */
extern struct symbol * symbol_hash[SYMBOL_HASHSIZE];
struct symbol * sym_lookup(const char *name, int flags);
struct symbol * sym_find(const char *name);
const char * sym_expand_string_value(const char *in);
const char * sym_escape_string_value(const char *in);
struct symbol ** sym_re_search(const char *pattern);
const char * sym_type_name(enum symbol_type type);
void sym_calc_value(struct symbol *sym);
enum symbol_type sym_get_type(struct symbol *sym);
bool sym_tristate_within_range(struct symbol *sym,tristate tri);
bool sym_set_tristate_value(struct symbol *sym,tristate tri);
tristate sym_toggle_tristate_value(struct symbol *sym);
bool sym_string_valid(struct symbol *sym, const char *newval);
bool sym_string_within_range(struct symbol *sym, const char *str);
bool sym_set_string_value(struct symbol *sym, const char *newval);
bool sym_is_changable(struct symbol *sym);
struct property * sym_get_choice_prop(struct symbol *sym);
const char * sym_get_string_value(struct symbol *sym);
const char * prop_get_type_name(enum prop_type type);
/* expr.c */
void expr_print(struct expr *e, void (*fn)(void *, struct symbol *, const char *), void *data, int prevtoken);
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