Re: [PATCH 4/6] mm: Replace PF_MEMALLOC_NOFS with memalloc_nofs

Michal Hocko
2020-06-25T13:35:08Z

On Thu 25-06-20 12:31:20, Matthew Wilcox wrote:
> We're short on PF_* flags, so make memalloc_nofs its own bit where we
> have plenty of space.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

forgot to add
Acked-by: Michal Hocko <mhocko@suse.com>

> ---
> fs/iomap/buffered-io.c | 2 +-
> include/linux/sched.h | 2 +-
> include/linux/sched/mm.h | 13 ++++++-------
> 3 files changed, 8 insertions(+), 9 deletions(-)
>
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index bcfc288dba3f..87d66c13bf5c 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -1502,7 +1502,7 @@ iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
> * Given that we do not allow direct reclaim to call us, we should
> * never be called in a recursive filesystem reclaim context.
> */
> - if (WARN_ON_ONCE(current->flags & PF_MEMALLOC_NOFS))
> + if (WARN_ON_ONCE(current->memalloc_nofs))
> goto redirty;
>
> /*
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index cf18a3d2bc4c..eaf36ae1fde2 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -802,6 +802,7 @@ struct task_struct {
> unsigned in_memstall:1;
> #endif
> unsigned memalloc_noio:1;
> + unsigned memalloc_nofs:1;
>
> unsigned long atomic_flags; /* Flags requiring atomic access. */
>
> @@ -1505,7 +1506,6 @@ extern struct pid *cad_pid;
> #define PF_NOFREEZE 0x00008000 /* This thread should not be frozen */
> #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_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 b0089eadc367..08bc9d0606a8 100644
> --- a/include/linux/sched/mm.h
> +++ b/include/linux/sched/mm.h
> @@ -175,20 +175,19 @@ static inline bool in_vfork(struct task_struct *tsk)
>
> /*
> * Applies per-task gfp context to the given allocation flags.
> - * 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_NOFS | PF_MEMALLOC_NOCMA) ||
> - current->memalloc_noio)) {
> + if (unlikely((current->flags & PF_MEMALLOC_NOCMA) ||
> + current->memalloc_noio || current->memalloc_nofs)) {
> /*
> * NOIO implies both NOIO and NOFS and it is a weaker context
> * so always make sure it makes precedence
> */
> if (current->memalloc_noio)
> flags &= ~(__GFP_IO | __GFP_FS);
> - else if (current->flags & PF_MEMALLOC_NOFS)
> + else if (current->memalloc_nofs)
> flags &= ~__GFP_FS;
> #ifdef CONFIG_CMA
> if (current->flags & PF_MEMALLOC_NOCMA)
> @@ -254,8 +253,8 @@ static inline void memalloc_noio_restore(unsigned int flags)
> */
> static inline unsigned int memalloc_nofs_save(void)
> {
> - unsigned int flags = current->flags & PF_MEMALLOC_NOFS;
> - current->flags |= PF_MEMALLOC_NOFS;
> + unsigned int flags = current->memalloc_nofs;
> + current->memalloc_nofs = 1;
> return flags;
> }
>
> @@ -269,7 +268,7 @@ static inline unsigned int memalloc_nofs_save(void)
> */
> static inline void memalloc_nofs_restore(unsigned int flags)
> {
> - current->flags = (current->flags & ~PF_MEMALLOC_NOFS) | flags;
> + current->memalloc_nofs = flags ? 1 : 0;
> }
>
> static inline unsigned int memalloc_noreclaim_save(void)
> --
> 2.27.0

--
Michal Hocko
SUSE Labs