| Message ID | 20240724085544.299090-3-21cnbao@gmail.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm: clarify nofail memory allocation | expand |
On Wed 24-07-24 20:55:41, Barry Song wrote: > From: Barry Song <v-songbaohua@oppo.com> > > Non-blocking allocation with __GFP_NOFAIL is not supported and may > still result in NULL pointers (if we don't return NULL, we result > in busy-loop within non-sleepable contexts): > > static inline struct page * > __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > struct alloc_context *ac) > { > ... > /* > * Make sure that __GFP_NOFAIL request doesn't leak out and make sure > * we always retry > */ > if (gfp_mask & __GFP_NOFAIL) { > /* > * All existing users of the __GFP_NOFAIL are blockable, so warn > * of any new users that actually require GFP_NOWAIT > */ > if (WARN_ON_ONCE_GFP(!can_direct_reclaim, gfp_mask)) > goto fail; > ... > } > ... > fail: > warn_alloc(gfp_mask, ac->nodemask, > "page allocation failure: order:%u", order); > got_pg: > return page; > } > > Highlight this in the documentation of __GFP_NOFAIL so that non-mm > subsystems can reject any illegal usage of __GFP_NOFAIL with > GFP_ATOMIC, GFP_NOWAIT, etc. > > Signed-off-by: Barry Song <v-songbaohua@oppo.com> Acked-by: Michal Hocko <mhocko@suse.com> > --- > include/linux/gfp_types.h | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/include/linux/gfp_types.h b/include/linux/gfp_types.h > index 313be4ad79fd..0dad2c7914be 100644 > --- a/include/linux/gfp_types.h > +++ b/include/linux/gfp_types.h > @@ -246,6 +246,8 @@ enum { > * cannot handle allocation failures. The allocation could block > * indefinitely but will never return with failure. Testing for > * failure is pointless. > + * It _must_ be blockable and used together with __GFP_DIRECT_RECLAIM. > + * It should _never_ be used in non-sleepable contexts. > * New users should be evaluated carefully (and the flag should be > * used only when there is no reasonable failure policy) but it is > * definitely preferable to use the flag rather than opencode endless > -- > 2.34.1 Do you think the following addendum should be folded in just for completness? diff --git a/include/linux/gfp_types.h b/include/linux/gfp_types.h index 313be4ad79fd..d024cfd1af8e 100644 --- a/include/linux/gfp_types.h +++ b/include/linux/gfp_types.h @@ -215,7 +215,8 @@ enum { * the caller still has to check for failures) while costly requests try to be * not disruptive and back off even without invoking the OOM killer. * The following three modifiers might be used to override some of these - * implicit rules. + * implicit rules. Please note that all of them must be used along with + * %__GFP_DIRECT_RECLAIM flag. * * %__GFP_NORETRY: The VM implementation will try only very lightweight * memory direct reclaim to get some memory under memory pressure (thus
On Wed, 24 Jul 2024, Barry Song wrote:\n >From: Barry Song <v-songbaohua@oppo.com> > >Non-blocking allocation with __GFP_NOFAIL is not supported and may >still result in NULL pointers (if we don't return NULL, we result >in busy-loop within non-sleepable contexts): > >static inline struct page * >__alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > struct alloc_context *ac) >{ > ... > /* > * Make sure that __GFP_NOFAIL request doesn't leak out and make sure > * we always retry > */ > if (gfp_mask & __GFP_NOFAIL) { > /* > * All existing users of the __GFP_NOFAIL are blockable, so warn > * of any new users that actually require GFP_NOWAIT > */ > if (WARN_ON_ONCE_GFP(!can_direct_reclaim, gfp_mask)) > goto fail; > ... > } > ... >fail: > warn_alloc(gfp_mask, ac->nodemask, > "page allocation failure: order:%u", order); >got_pg: > return page; >} > >Highlight this in the documentation of __GFP_NOFAIL so that non-mm >subsystems can reject any illegal usage of __GFP_NOFAIL with >GFP_ATOMIC, GFP_NOWAIT, etc. > Acked-by: Davidlohr Bueso <dave@stgolabs.net>
diff --git a/include/linux/gfp_types.h b/include/linux/gfp_types.h index 313be4ad79fd..0dad2c7914be 100644 --- a/include/linux/gfp_types.h +++ b/include/linux/gfp_types.h @@ -246,6 +246,8 @@ enum { * cannot handle allocation failures. The allocation could block * indefinitely but will never return with failure. Testing for * failure is pointless. + * It _must_ be blockable and used together with __GFP_DIRECT_RECLAIM. + * It should _never_ be used in non-sleepable contexts. * New users should be evaluated carefully (and the flag should be * used only when there is no reasonable failure policy) but it is * definitely preferable to use the flag rather than opencode endless