On Thu 25-06-20 12:31:17, Matthew Wilcox wrote: > We're short on PF_* flags, so make memalloc_noio its own bit where we > have plenty of space.
I do not mind moving that outside of the PF_* space. Unless I misremember all flags in this space were intented to be set only on the current which rules out any RMW races and therefore they can be lockless. I am not sure this holds for the bitfield you are adding this to. At least in_memstall seem to be set on external task as well. But this would require double checking. Maybe that is not really intended or just a bug. > Signed-off-by: Matthew Wilcox (Oracle) <[email protected]> > --- > drivers/block/loop.c | 3 ++- > drivers/md/dm-zoned-metadata.c | 5 ++--- > include/linux/sched.h | 2 +- > include/linux/sched/mm.h | 30 +++++++++++++++++++++++------- > kernel/sys.c | 8 +++----- > 5 files changed, 31 insertions(+), 17 deletions(-) > > diff --git a/drivers/block/loop.c b/drivers/block/loop.c > index 475e1a738560..c8742e25e58a 100644 > --- a/drivers/block/loop.c > +++ b/drivers/block/loop.c > @@ -52,6 +52,7 @@ > #include <linux/module.h> > #include <linux/moduleparam.h> > #include <linux/sched.h> > +#include <linux/sched/mm.h> > #include <linux/fs.h> > #include <linux/file.h> > #include <linux/stat.h> > @@ -929,7 +930,7 @@ static void loop_unprepare_queue(struct loop_device *lo) > > static int loop_kthread_worker_fn(void *worker_ptr) > { > - current->flags |= PF_LOCAL_THROTTLE | PF_MEMALLOC_NOIO; > + set_current_io_flusher(); > return kthread_worker_fn(worker_ptr); > } > > diff --git a/drivers/md/dm-zoned-metadata.c b/drivers/md/dm-zoned-metadata.c > index 130b5a6d9f12..1c5ae674ba20 100644 > --- a/drivers/md/dm-zoned-metadata.c > +++ b/drivers/md/dm-zoned-metadata.c > @@ -1599,9 +1599,8 @@ static int dmz_update_zone(struct dmz_metadata *zmd, > struct dm_zone *zone) > > /* > * Get zone information from disk. Since blkdev_report_zones() uses > - * GFP_KERNEL by default for memory allocations, set the per-task > - * PF_MEMALLOC_NOIO flag so that all allocations are done as if > - * GFP_NOIO was specified. > + * GFP_KERNEL by default for memory allocations, use > + * memalloc_noio_save() to prevent recursion into the driver. > */ > noio_flag = memalloc_noio_save(); > ret = blkdev_report_zones(dev->bdev, dmz_start_sect(zmd, zone), 1, > diff --git a/include/linux/sched.h b/include/linux/sched.h > index b62e6aaf28f0..cf18a3d2bc4c 100644 > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -801,6 +801,7 @@ struct task_struct { > /* Stalled due to lack of memory */ > unsigned in_memstall:1; > #endif > + unsigned memalloc_noio:1; > > unsigned long atomic_flags; /* Flags requiring atomic > access. */ > > @@ -1505,7 +1506,6 @@ extern struct pid *cad_pid; > #define PF_FROZEN 0x00010000 /* Frozen for system suspend */ > #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_LOCAL_THROTTLE 0x00100000 /* Throttle writes only against > the bdi I write to, > * I am cleaning dirty pages > from some other bdi. */ > #define PF_KTHREAD 0x00200000 /* I am a kernel thread */ > diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h > index 480a4d1b7dd8..1a7e1ab1be85 100644 > --- a/include/linux/sched/mm.h > +++ b/include/linux/sched/mm.h > @@ -175,19 +175,18 @@ static inline bool in_vfork(struct task_struct *tsk) > > /* > * Applies per-task gfp context to the given allocation flags. > - * PF_MEMALLOC_NOIO implies GFP_NOIO > * PF_MEMALLOC_NOFS implies GFP_NOFS > * PF_MEMALLOC_NOCMA implies no allocation from CMA region. > */ > static inline gfp_t current_gfp_context(gfp_t flags) > { > - if (unlikely(current->flags & > - (PF_MEMALLOC_NOIO | PF_MEMALLOC_NOFS | > PF_MEMALLOC_NOCMA))) { > + if (unlikely(current->flags & (PF_MEMALLOC_NOFS | PF_MEMALLOC_NOCMA) || > + current->memalloc_noio)) { > /* > * NOIO implies both NOIO and NOFS and it is a weaker context > * so always make sure it makes precedence > */ > - if (current->flags & PF_MEMALLOC_NOIO) > + if (current->memalloc_noio) > flags &= ~(__GFP_IO | __GFP_FS); > else if (current->flags & PF_MEMALLOC_NOFS) > flags &= ~__GFP_FS; > @@ -224,8 +223,8 @@ static inline void fs_reclaim_release(gfp_t gfp_mask) { } > */ > static inline unsigned int memalloc_noio_save(void) > { > - unsigned int flags = current->flags & PF_MEMALLOC_NOIO; > - current->flags |= PF_MEMALLOC_NOIO; > + unsigned int flags = current->memalloc_noio; > + current->memalloc_noio = 1; > return flags; > } > > @@ -239,7 +238,7 @@ static inline unsigned int memalloc_noio_save(void) > */ > static inline void memalloc_noio_restore(unsigned int flags) > { > - current->flags = (current->flags & ~PF_MEMALLOC_NOIO) | flags; > + current->memalloc_noio = flags ? 1 : 0; > } > > /** > @@ -309,6 +308,23 @@ static inline void memalloc_nocma_restore(unsigned int > flags) > } > #endif > > +static inline void set_current_io_flusher(void) > +{ > + current->flags |= PF_LOCAL_THROTTLE; > + current->memalloc_noio = 1; > +} > + > +static inline void clear_current_io_flusher(void) > +{ > + current->flags &= ~PF_LOCAL_THROTTLE; > + current->memalloc_noio = 0; > +} > + > +static inline bool get_current_io_flusher(void) > +{ > + return current->flags & PF_LOCAL_THROTTLE; > +} > + > #ifdef CONFIG_MEMCG > /** > * memalloc_use_memcg - Starts the remote memcg charging scope. > diff --git a/kernel/sys.c b/kernel/sys.c > index 00a96746e28a..78c90d1e92f4 100644 > --- a/kernel/sys.c > +++ b/kernel/sys.c > @@ -2275,8 +2275,6 @@ int __weak arch_prctl_spec_ctrl_set(struct task_struct > *t, unsigned long which, > return -EINVAL; > } > > -#define PR_IO_FLUSHER (PF_MEMALLOC_NOIO | PF_LOCAL_THROTTLE) > - > SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3, > unsigned long, arg4, unsigned long, arg5) > { > @@ -2512,9 +2510,9 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, > arg2, unsigned long, arg3, > return -EINVAL; > > if (arg2 == 1) > - current->flags |= PR_IO_FLUSHER; > + set_current_io_flusher(); > else if (!arg2) > - current->flags &= ~PR_IO_FLUSHER; > + clear_current_io_flusher(); > else > return -EINVAL; > break; > @@ -2525,7 +2523,7 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, > arg2, unsigned long, arg3, > if (arg2 || arg3 || arg4 || arg5) > return -EINVAL; > > - error = (current->flags & PR_IO_FLUSHER) == PR_IO_FLUSHER; > + error = get_current_io_flusher(); > break; > default: > error = -EINVAL; > -- > 2.27.0 > -- Michal Hocko SUSE Labs
