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

[Michal Hocko]

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@xxxxxxxxxxxxx>

forgot to add
Acked-by: Michal Hocko <mhocko@xxxxxxxx>

> ---
>  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