| Message ID | 20170306131408.9828-5-mhocko@kernel.org (mailing list archive) |
|---|---|
| State | Not Applicable, archived |
| Headers | show |
On Mon, 6 Mar 2017 14:14:05 +0100 Michal Hocko <mhocko@kernel.org> wrote: > From: Michal Hocko <mhocko@suse.com> > > GFP_NOFS context is used for the following 5 reasons currently > - to prevent from deadlocks when the lock held by the allocation > context would be needed during the memory reclaim > - to prevent from stack overflows during the reclaim because > the allocation is performed from a deep context already > - to prevent lockups when the allocation context depends on > other reclaimers to make a forward progress indirectly > - just in case because this would be safe from the fs POV > - silence lockdep false positives > > Unfortunately overuse of this allocation context brings some problems > to the MM. Memory reclaim is much weaker (especially during heavy FS > metadata workloads), OOM killer cannot be invoked because the MM layer > doesn't have enough information about how much memory is freeable by the > FS layer. > > In many cases it is far from clear why the weaker context is even used > and so it might be used unnecessarily. We would like to get rid of > those as much as possible. One way to do that is to use the flag in > scopes rather than isolated cases. Such a scope is declared when really > necessary, tracked per task and all the allocation requests from within > the context will simply inherit the GFP_NOFS semantic. > > Not only this is easier to understand and maintain because there are > much less problematic contexts than specific allocation requests, this > also helps code paths where FS layer interacts with other layers (e.g. > crypto, security modules, MM etc...) and there is no easy way to convey > the allocation context between the layers. > > Introduce memalloc_nofs_{save,restore} API to control the scope > of GFP_NOFS allocation context. This is basically copying > memalloc_noio_{save,restore} API we have for other restricted allocation > context GFP_NOIO. The PF_MEMALLOC_NOFS flag already exists and it is > just an alias for PF_FSTRANS which has been xfs specific until recently. > There are no more PF_FSTRANS users anymore so let's just drop it. > > PF_MEMALLOC_NOFS is now checked in the MM layer and drops __GFP_FS > implicitly same as PF_MEMALLOC_NOIO drops __GFP_IO. memalloc_noio_flags > is renamed to current_gfp_context because it now cares about both > PF_MEMALLOC_NOFS and PF_MEMALLOC_NOIO contexts. Xfs code paths preserve > their semantic. kmem_flags_convert() doesn't need to evaluate the flag > anymore. > > This patch shouldn't introduce any functional changes. > > Let's hope that filesystems will drop direct GFP_NOFS (resp. ~__GFP_FS) > usage as much as possible and only use a properly documented > memalloc_nofs_{save,restore} checkpoints where they are appropriate. > > .... > > --- a/include/linux/gfp.h > +++ b/include/linux/gfp.h > @@ -210,8 +210,16 @@ struct vm_area_struct; > * > * GFP_NOIO will use direct reclaim to discard clean pages or slab pages > * that do not require the starting of any physical IO. > + * Please try to avoid using this flag directly and instead use > + * memalloc_noio_{save,restore} to mark the whole scope which cannot > + * perform any IO with a short explanation why. All allocation requests > + * will inherit GFP_NOIO implicitly. > * > * GFP_NOFS will use direct reclaim but will not use any filesystem interfaces. > + * Please try to avoid using this flag directly and instead use > + * memalloc_nofs_{save,restore} to mark the whole scope which cannot/shouldn't > + * recurse into the FS layer with a short explanation why. All allocation > + * requests will inherit GFP_NOFS implicitly. I wonder if these are worth a checkpatch rule. -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Mon 06-03-17 13:22:14, Andrew Morton wrote: > On Mon, 6 Mar 2017 14:14:05 +0100 Michal Hocko <mhocko@kernel.org> wrote: [...] > > --- a/include/linux/gfp.h > > +++ b/include/linux/gfp.h > > @@ -210,8 +210,16 @@ struct vm_area_struct; > > * > > * GFP_NOIO will use direct reclaim to discard clean pages or slab pages > > * that do not require the starting of any physical IO. > > + * Please try to avoid using this flag directly and instead use > > + * memalloc_noio_{save,restore} to mark the whole scope which cannot > > + * perform any IO with a short explanation why. All allocation requests > > + * will inherit GFP_NOIO implicitly. > > * > > * GFP_NOFS will use direct reclaim but will not use any filesystem interfaces. > > + * Please try to avoid using this flag directly and instead use > > + * memalloc_nofs_{save,restore} to mark the whole scope which cannot/shouldn't > > + * recurse into the FS layer with a short explanation why. All allocation > > + * requests will inherit GFP_NOFS implicitly. > > I wonder if these are worth a checkpatch rule. I am not really sure, to be honest. This may easilly end up people replacing do_alloc(GFP_NOFS) with memalloc_nofs_save() do_alloc(GFP_KERNEL) memalloc_nofs_restore() which doesn't make any sense of course. From my experience, people tend to do stupid things just to silent checkpatch warnings very often. Moreover I believe we need to do the transition to the new api first before we can push back on the explicit GFP_NOFS usage. Maybe then we can think about the a checkpatch warning.
On Tue, Mar 07, 2017 at 04:09:56PM +0100, Michal Hocko wrote: > On Mon 06-03-17 13:22:14, Andrew Morton wrote: > > On Mon, 6 Mar 2017 14:14:05 +0100 Michal Hocko <mhocko@kernel.org> wrote: > [...] > > > --- a/include/linux/gfp.h > > > +++ b/include/linux/gfp.h > > > @@ -210,8 +210,16 @@ struct vm_area_struct; > > > * > > > * GFP_NOIO will use direct reclaim to discard clean pages or slab pages > > > * that do not require the starting of any physical IO. > > > + * Please try to avoid using this flag directly and instead use > > > + * memalloc_noio_{save,restore} to mark the whole scope which cannot > > > + * perform any IO with a short explanation why. All allocation requests > > > + * will inherit GFP_NOIO implicitly. > > > * > > > * GFP_NOFS will use direct reclaim but will not use any filesystem interfaces. > > > + * Please try to avoid using this flag directly and instead use > > > + * memalloc_nofs_{save,restore} to mark the whole scope which cannot/shouldn't > > > + * recurse into the FS layer with a short explanation why. All allocation > > > + * requests will inherit GFP_NOFS implicitly. > > > > I wonder if these are worth a checkpatch rule. > > I am not really sure, to be honest. This may easilly end up people > replacing > > do_alloc(GFP_NOFS) > > with > > memalloc_nofs_save() > do_alloc(GFP_KERNEL) > memalloc_nofs_restore() > > which doesn't make any sense of course. From my experience, people tend > to do stupid things just to silent checkpatch warnings very often. > Moreover I believe we need to do the transition to the new api first > before we can push back on the explicit GFP_NOFS usage. Maybe then we > can think about the a checkpatch warning. I agree will all your objections against adding that to checkpatch, at this point it's less harmful to use GFP_NOFS. -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/xfs/kmem.h b/fs/xfs/kmem.h index d973dbfc2bfa..ae08cfd9552a 100644 --- a/fs/xfs/kmem.h +++ b/fs/xfs/kmem.h @@ -50,7 +50,7 @@ kmem_flags_convert(xfs_km_flags_t flags) lflags = GFP_ATOMIC | __GFP_NOWARN; } else { lflags = GFP_KERNEL | __GFP_NOWARN; - if ((current->flags & PF_MEMALLOC_NOFS) || (flags & KM_NOFS)) + if (flags & KM_NOFS) lflags &= ~__GFP_FS; } diff --git a/include/linux/gfp.h b/include/linux/gfp.h index 978232a3b4ae..2bfcfd33e476 100644 --- a/include/linux/gfp.h +++ b/include/linux/gfp.h @@ -210,8 +210,16 @@ struct vm_area_struct; * * GFP_NOIO will use direct reclaim to discard clean pages or slab pages * that do not require the starting of any physical IO. + * Please try to avoid using this flag directly and instead use + * memalloc_noio_{save,restore} to mark the whole scope which cannot + * perform any IO with a short explanation why. All allocation requests + * will inherit GFP_NOIO implicitly. * * GFP_NOFS will use direct reclaim but will not use any filesystem interfaces. + * Please try to avoid using this flag directly and instead use + * memalloc_nofs_{save,restore} to mark the whole scope which cannot/shouldn't + * recurse into the FS layer with a short explanation why. All allocation + * requests will inherit GFP_NOFS implicitly. * * GFP_USER is for userspace allocations that also need to be directly * accessibly by the kernel or hardware. It is typically used by hardware diff --git a/include/linux/sched.h b/include/linux/sched.h index 4528f7c9789f..9c3ee2281a56 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1211,9 +1211,9 @@ extern struct pid *cad_pid; #define PF_USED_ASYNC 0x00004000 /* Used async_schedule*(), used by module init */ #define PF_NOFREEZE 0x00008000 /* This thread should not be frozen */ #define PF_FROZEN 0x00010000 /* Frozen for system suspend */ -#define PF_FSTRANS 0x00020000 /* Inside a filesystem transaction */ -#define PF_KSWAPD 0x00040000 /* I am kswapd */ -#define PF_MEMALLOC_NOIO 0x00080000 /* Allocating memory without IO involved */ +#define PF_KSWAPD 0x00020000 /* I am kswapd */ +#define PF_MEMALLOC_NOFS 0x00040000 /* All allocation requests will inherit GFP_NOFS */ +#define PF_MEMALLOC_NOIO 0x00080000 /* All allocation requests will inherit GFP_NOIO */ #define PF_LESS_THROTTLE 0x00100000 /* Throttle me less: I clean memory */ #define PF_KTHREAD 0x00200000 /* I am a kernel thread */ #define PF_RANDOMIZE 0x00400000 /* Randomize virtual address space */ @@ -1224,8 +1224,6 @@ extern struct pid *cad_pid; #define PF_FREEZER_SKIP 0x40000000 /* Freezer should not count it as freezable */ #define PF_SUSPEND_TASK 0x80000000 /* This thread called freeze_processes() and should not be frozen */ -#define PF_MEMALLOC_NOFS PF_FSTRANS /* Transition to a more generic GFP_NOFS scope semantic */ - /* * Only the _current_ task can read/write to tsk->flags, but other * tasks can access tsk->flags in readonly mode for example diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h index 830953ebb391..9daabe138c99 100644 --- a/include/linux/sched/mm.h +++ b/include/linux/sched/mm.h @@ -149,13 +149,21 @@ static inline bool in_vfork(struct task_struct *tsk) return ret; } -/* __GFP_IO isn't allowed if PF_MEMALLOC_NOIO is set in current->flags - * __GFP_FS is also cleared as it implies __GFP_IO. +/* + * Applies per-task gfp context to the given allocation flags. + * PF_MEMALLOC_NOIO implies GFP_NOIO + * PF_MEMALLOC_NOFS implies GFP_NOFS */ -static inline gfp_t memalloc_noio_flags(gfp_t flags) +static inline gfp_t current_gfp_context(gfp_t flags) { + /* + * NOIO implies both NOIO and NOFS and it is a weaker context + * so always make sure it makes precendence + */ if (unlikely(current->flags & PF_MEMALLOC_NOIO)) flags &= ~(__GFP_IO | __GFP_FS); + else if (unlikely(current->flags & PF_MEMALLOC_NOFS)) + flags &= ~__GFP_FS; return flags; } @@ -171,4 +179,16 @@ static inline void memalloc_noio_restore(unsigned int flags) current->flags = (current->flags & ~PF_MEMALLOC_NOIO) | flags; } +static inline unsigned int memalloc_nofs_save(void) +{ + unsigned int flags = current->flags & PF_MEMALLOC_NOFS; + current->flags |= PF_MEMALLOC_NOFS; + return flags; +} + +static inline void memalloc_nofs_restore(unsigned int flags) +{ + current->flags = (current->flags & ~PF_MEMALLOC_NOFS) | flags; +} + #endif /* _LINUX_SCHED_MM_H */ diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index b169339541f5..84afa9f19452 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -2864,7 +2864,7 @@ static void __lockdep_trace_alloc(gfp_t gfp_mask, unsigned long flags) if (unlikely(!debug_locks)) return; - gfp_mask = memalloc_noio_flags(gfp_mask); + gfp_mask = current_gfp_context(gfp_mask); /* no reclaim without waiting on it */ if (!(gfp_mask & __GFP_DIRECT_RECLAIM)) @@ -2875,7 +2875,7 @@ static void __lockdep_trace_alloc(gfp_t gfp_mask, unsigned long flags) return; /* We're only interested __GFP_FS allocations for now */ - if (!(gfp_mask & __GFP_FS)) + if (!(gfp_mask & __GFP_FS) || (curr->flags & PF_MEMALLOC_NOFS)) return; /* @@ -3861,7 +3861,7 @@ EXPORT_SYMBOL_GPL(lock_unpin_lock); void lockdep_set_current_reclaim_state(gfp_t gfp_mask) { - current->lockdep_reclaim_gfp = memalloc_noio_flags(gfp_mask); + current->lockdep_reclaim_gfp = current_gfp_context(gfp_mask); } void lockdep_clear_current_reclaim_state(void) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index eaa64d2ffdc5..f7531a93a0d0 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -3966,10 +3966,12 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order, goto out; /* - * Runtime PM, block IO and its error handling path can deadlock - * because I/O on the device might not complete. + * Apply scoped allocation constrains. This is mainly about + * GFP_NOFS resp. GFP_NOIO which has to be inherited for all + * allocation requests from a particular context which has + * been marked by memalloc_no{fs,io}_{save,restore} */ - alloc_mask = memalloc_noio_flags(gfp_mask); + alloc_mask = current_gfp_context(gfp_mask); ac.spread_dirty_pages = false; /* @@ -7423,7 +7425,7 @@ int alloc_contig_range(unsigned long start, unsigned long end, .zone = page_zone(pfn_to_page(start)), .mode = MIGRATE_SYNC, .ignore_skip_hint = true, - .gfp_mask = memalloc_noio_flags(gfp_mask), + .gfp_mask = current_gfp_context(gfp_mask), }; INIT_LIST_HEAD(&cc.migratepages); diff --git a/mm/vmscan.c b/mm/vmscan.c index bc8031ef994d..7d8590392f3d 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2950,7 +2950,7 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order, unsigned long nr_reclaimed; struct scan_control sc = { .nr_to_reclaim = SWAP_CLUSTER_MAX, - .gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)), + .gfp_mask = (gfp_mask = current_gfp_context(gfp_mask)), .reclaim_idx = gfp_zone(gfp_mask), .order = order, .nodemask = nodemask, @@ -3030,7 +3030,7 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg, int nid; struct scan_control sc = { .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX), - .gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) | + .gfp_mask = (current_gfp_context(gfp_mask) & GFP_RECLAIM_MASK) | (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK), .reclaim_idx = MAX_NR_ZONES - 1, .target_mem_cgroup = memcg, @@ -3725,7 +3725,7 @@ static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned in int classzone_idx = gfp_zone(gfp_mask); struct scan_control sc = { .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX), - .gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)), + .gfp_mask = (gfp_mask = current_gfp_context(gfp_mask)), .order = order, .priority = NODE_RECLAIM_PRIORITY, .may_writepage = !!(node_reclaim_mode & RECLAIM_WRITE),