Re: [RFC PATCH 1/3] mm: teach mm by current context info to not doI/O during memory allocation

[Minchan Kim]

On Mon, Oct 15, 2012 at 01:14:17PM +0800, Ming Lei wrote:
> This patch introduces PF_MEMALLOC_NOIO on process flag('flags' field of
> 'struct task_struct'), so that the flag can be set by one task
> to avoid doing I/O inside memory allocation in the task's context.
> 
> The patch trys to solve one deadlock problem caused by block device,
> and the problem can be occured at least in the below situations:
> 
> - during block device runtime resume situation, if memory allocation
> with GFP_KERNEL is called inside runtime resume callback of any one
> of its ancestors(or the block device itself), the deadlock may be
> triggered inside the memory allocation since it might not complete
> until the block device becomes active and the involed page I/O finishes.
> The situation is pointed out first by Alan Stern. It is not a good
> approach to convert all GFP_KERNEL in the path into GFP_NOIO because
> several subsystems may be involved(for example, PCI, USB and SCSI may
> be involved for usb mass stoarage device)

Couldn't we expand pm_restrict_gfp_mask to cover resume path as well as
suspend path?

> 
> - during error handling situation of usb mass storage deivce, USB
> bus reset will be put on the device, so there shouldn't have any
> memory allocation with GFP_KERNEL during USB bus reset, otherwise
> the deadlock similar with above may be triggered. Unfortunately, any
> usb device may include one mass storage interface in theory, so it
> requires all usb interface drivers to handle the situation. In fact,
> most usb drivers don't know how to handle bus reset on the device
> and don't provide .pre_set() and .post_reset() callback at all, so
> USB core has to unbind and bind driver for these devices. So it
> is still not practical to resort to GFP_NOIO for solving the problem.

I hope this case could be handled by usb core like usb_restrict_gfp_mask
rather than adding new branch on fast path.

> 
> Also the introduced solution can be used by block subsystem or block
> drivers too, for example, set the PF_MEMALLOC_NOIO flag before doing
> actual I/O transfer.
> 
> Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
> Cc: Oliver Neukum <oneukum@xxxxxxx>
> Cc: Jiri Kosina <jiri.kosina@xxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Mel Gorman <mel@xxxxxxxxx>
> Cc: Minchan Kim <minchan@xxxxxxxxxx>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: "Rafael J. Wysocki" <rjw@xxxxxxx>
> Cc: linux-mm <linux-mm@xxxxxxxxx>
> 
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxxxxx>
> ---
>  include/linux/sched.h |    5 +++++
>  mm/page_alloc.c       |    2 ++
>  2 files changed, 7 insertions(+)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index f6961c9..33be290 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1811,6 +1811,7 @@ extern void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t *
>  #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_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 */
> @@ -1848,6 +1849,10 @@ extern void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t *
>  #define tsk_used_math(p) ((p)->flags & PF_USED_MATH)
>  #define used_math() tsk_used_math(current)
>  
> +#define tsk_memalloc_no_io(p) ((p)->flags & PF_MEMALLOC_NOIO)
> +#define tsk_memalloc_allow_io(p) do { (p)->flags &= ~PF_MEMALLOC_NOIO; } while (0)
> +#define tsk_memalloc_forbid_io(p) do { (p)->flags |= PF_MEMALLOC_NOIO; } while (0)
> +
>  /*
>   * task->jobctl flags
>   */
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 8e1be1c..e15381f 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2596,6 +2596,8 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
>  	int alloc_flags = ALLOC_WMARK_LOW|ALLOC_CPUSET;
>  
>  	gfp_mask &= gfp_allowed_mask;
> +	if (unlikely(tsk_memalloc_no_io(current)))
> +		gfp_mask &= ~GFP_IOFS;
>  
>  	lockdep_trace_alloc(gfp_mask);
>  
> -- 
> 1.7.9.5
> 

-- 
Kind Regards,
Minchan Kim
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