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* [PATCH] Add prctl support for controlling mem reclaim V3
@ 2019-11-08 18:53 Mike Christie
  2019-11-09  2:09 ` Damien Le Moal
                   ` (2 more replies)
  0 siblings, 3 replies; 5+ messages in thread
From: Mike Christie @ 2019-11-08 18:53 UTC (permalink / raw)
  To: mhocko, david, linux-mm, linux-kernel, linux-scsi, linux-fsdevel,
	linux-block, martin, Damien.LeMoal
  Cc: Mike Christie

There are several storage drivers like dm-multipath, iscsi, tcmu-runner,
amd nbd that have userspace components that can run in the IO path. For
example, iscsi and nbd's userspace deamons may need to recreate a socket
and/or send IO on it, and dm-multipath's daemon multipathd may need to
send SG IO or read/write IO to figure out the state of paths and re-set
them up.

In the kernel these drivers have access to GFP_NOIO/GFP_NOFS and the
memalloc_*_save/restore functions to control the allocation behavior,
but for userspace we would end up hitting an allocation that ended up
writing data back to the same device we are trying to allocate for.
The device is then in a state of deadlock, because to execute IO the
device needs to allocate memory, but to allocate memory the memory
layers want execute IO to the device.

Here is an example with nbd using a local userspace daemon that performs
network IO to a remote server. We are using XFS on top of the nbd device,
but it can happen with any FS or other modules layered on top of the nbd
device that can write out data to free memory.  Here a nbd daemon helper
thread, msgr-worker-1, is performing a write/sendmsg on a socket to execute
a request. This kicks off a reclaim operation which results in a WRITE to
the nbd device and the nbd thread calling back into the mm layer.

[ 1626.609191] msgr-worker-1   D    0  1026      1 0x00004000
[ 1626.609193] Call Trace:
[ 1626.609195]  ? __schedule+0x29b/0x630
[ 1626.609197]  ? wait_for_completion+0xe0/0x170
[ 1626.609198]  schedule+0x30/0xb0
[ 1626.609200]  schedule_timeout+0x1f6/0x2f0
[ 1626.609202]  ? blk_finish_plug+0x21/0x2e
[ 1626.609204]  ? _xfs_buf_ioapply+0x2e6/0x410
[ 1626.609206]  ? wait_for_completion+0xe0/0x170
[ 1626.609208]  wait_for_completion+0x108/0x170
[ 1626.609210]  ? wake_up_q+0x70/0x70
[ 1626.609212]  ? __xfs_buf_submit+0x12e/0x250
[ 1626.609214]  ? xfs_bwrite+0x25/0x60
[ 1626.609215]  xfs_buf_iowait+0x22/0xf0
[ 1626.609218]  __xfs_buf_submit+0x12e/0x250
[ 1626.609220]  xfs_bwrite+0x25/0x60
[ 1626.609222]  xfs_reclaim_inode+0x2e8/0x310
[ 1626.609224]  xfs_reclaim_inodes_ag+0x1b6/0x300
[ 1626.609227]  xfs_reclaim_inodes_nr+0x31/0x40
[ 1626.609228]  super_cache_scan+0x152/0x1a0
[ 1626.609231]  do_shrink_slab+0x12c/0x2d0
[ 1626.609233]  shrink_slab+0x9c/0x2a0
[ 1626.609235]  shrink_node+0xd7/0x470
[ 1626.609237]  do_try_to_free_pages+0xbf/0x380
[ 1626.609240]  try_to_free_pages+0xd9/0x1f0
[ 1626.609245]  __alloc_pages_slowpath+0x3a4/0xd30
[ 1626.609251]  ? ___slab_alloc+0x238/0x560
[ 1626.609254]  __alloc_pages_nodemask+0x30c/0x350
[ 1626.609259]  skb_page_frag_refill+0x97/0xd0
[ 1626.609274]  sk_page_frag_refill+0x1d/0x80
[ 1626.609279]  tcp_sendmsg_locked+0x2bb/0xdd0
[ 1626.609304]  tcp_sendmsg+0x27/0x40
[ 1626.609307]  sock_sendmsg+0x54/0x60
[ 1626.609308]  ___sys_sendmsg+0x29f/0x320
[ 1626.609313]  ? sock_poll+0x66/0xb0
[ 1626.609318]  ? ep_item_poll.isra.15+0x40/0xc0
[ 1626.609320]  ? ep_send_events_proc+0xe6/0x230
[ 1626.609322]  ? hrtimer_try_to_cancel+0x54/0xf0
[ 1626.609324]  ? ep_read_events_proc+0xc0/0xc0
[ 1626.609326]  ? _raw_write_unlock_irq+0xa/0x20
[ 1626.609327]  ? ep_scan_ready_list.constprop.19+0x218/0x230
[ 1626.609329]  ? __hrtimer_init+0xb0/0xb0
[ 1626.609331]  ? _raw_spin_unlock_irq+0xa/0x20
[ 1626.609334]  ? ep_poll+0x26c/0x4a0
[ 1626.609337]  ? tcp_tsq_write.part.54+0xa0/0xa0
[ 1626.609339]  ? release_sock+0x43/0x90
[ 1626.609341]  ? _raw_spin_unlock_bh+0xa/0x20
[ 1626.609342]  __sys_sendmsg+0x47/0x80
[ 1626.609347]  do_syscall_64+0x5f/0x1c0
[ 1626.609349]  ? prepare_exit_to_usermode+0x75/0xa0
[ 1626.609351]  entry_SYSCALL_64_after_hwframe+0x44/0xa9

This patch adds a new prctl command that daemons can use after they have
done their initial setup, and before they start to do allocations that
are in the IO path. It sets the PF_MEMALLOC_NOIO and PF_LESS_THROTTLE
flags so both userspace block and FS threads can use it to avoid the
allocation recursion and try to prevent from being throttled while
writing out data to free up memory.

Signed-off-by: Mike Christie <mchristi@redhat.com>
---
V3 
- Drop NOFS, set PF_LESS_THROTTLE and rename prctl flag to reflect it
is more general and can support both FS and block devices. Both fuse
and block device daemons, nbd and tcmu-runner, have been tested to
confirm the more restrictive PF_MEMALLOC_NOIO also works for fuse.

- Use CAP_SYS_RESOURCE instead of admin.

V2:
- Use prctl instead of procfs.
- Add support for NOFS for fuse.
- Check permissions.


 include/uapi/linux/capability.h |  1 +
 include/uapi/linux/prctl.h      |  4 ++++
 kernel/sys.c                    | 26 ++++++++++++++++++++++++++
 3 files changed, 31 insertions(+)

diff --git a/include/uapi/linux/capability.h b/include/uapi/linux/capability.h
index 240fdb9a60f6..272dc69fa080 100644
--- a/include/uapi/linux/capability.h
+++ b/include/uapi/linux/capability.h
@@ -301,6 +301,7 @@ struct vfs_ns_cap_data {
 /* Allow more than 64hz interrupts from the real-time clock */
 /* Override max number of consoles on console allocation */
 /* Override max number of keymaps */
+/* Control memory reclaim behavior */
 
 #define CAP_SYS_RESOURCE     24
 
diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
index 7da1b37b27aa..07b4f8131e36 100644
--- a/include/uapi/linux/prctl.h
+++ b/include/uapi/linux/prctl.h
@@ -234,4 +234,8 @@ struct prctl_mm_map {
 #define PR_GET_TAGGED_ADDR_CTRL		56
 # define PR_TAGGED_ADDR_ENABLE		(1UL << 0)
 
+/* Control reclaim behavior when allocating memory */
+#define PR_SET_IO_FLUSHER		57
+#define PR_GET_IO_FLUSHER		58
+
 #endif /* _LINUX_PRCTL_H */
diff --git a/kernel/sys.c b/kernel/sys.c
index a611d1d58c7d..08c6b682fa99 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -2486,6 +2486,32 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
 			return -EINVAL;
 		error = GET_TAGGED_ADDR_CTRL();
 		break;
+	case PR_SET_IO_FLUSHER:
+		if (!capable(CAP_SYS_RESOURCE))
+			return -EPERM;
+
+		if (arg3 || arg4 || arg5)
+			return -EINVAL;
+
+		if (arg2 == 1)
+			current->flags |= PF_MEMALLOC_NOIO | PF_LESS_THROTTLE;
+		else if (!arg2)
+			current->flags &= ~(PF_MEMALLOC_NOIO | PF_LESS_THROTTLE);
+		else
+			return -EINVAL;
+		break;
+	case PR_GET_IO_FLUSHER:
+		if (!capable(CAP_SYS_RESOURCE))
+			return -EPERM;
+
+		if (arg2 || arg3 || arg4 || arg5)
+			return -EINVAL;
+
+		if (current->flags & (PF_MEMALLOC_NOIO | PF_LESS_THROTTLE))
+			error = 1;
+		else
+			error = 0;
+		break;
 	default:
 		error = -EINVAL;
 		break;
-- 
2.20.1



^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [PATCH] Add prctl support for controlling mem reclaim V3
  2019-11-08 18:53 [PATCH] Add prctl support for controlling mem reclaim V3 Mike Christie
@ 2019-11-09  2:09 ` Damien Le Moal
  2019-11-09 19:47 ` Ilya Dryomov
  2019-11-11  9:32 ` Michal Hocko
  2 siblings, 0 replies; 5+ messages in thread
From: Damien Le Moal @ 2019-11-09  2:09 UTC (permalink / raw)
  To: Mike Christie, mhocko, david, linux-mm, linux-kernel, linux-scsi,
	linux-fsdevel, linux-block, martin, Masato Suzuki

On 2019/11/09 3:53, Mike Christie wrote:
> There are several storage drivers like dm-multipath, iscsi, tcmu-runner,
> amd nbd that have userspace components that can run in the IO path. For
> example, iscsi and nbd's userspace deamons may need to recreate a socket
> and/or send IO on it, and dm-multipath's daemon multipathd may need to
> send SG IO or read/write IO to figure out the state of paths and re-set
> them up.
> 
> In the kernel these drivers have access to GFP_NOIO/GFP_NOFS and the
> memalloc_*_save/restore functions to control the allocation behavior,
> but for userspace we would end up hitting an allocation that ended up
> writing data back to the same device we are trying to allocate for.
> The device is then in a state of deadlock, because to execute IO the
> device needs to allocate memory, but to allocate memory the memory
> layers want execute IO to the device.
> 
> Here is an example with nbd using a local userspace daemon that performs
> network IO to a remote server. We are using XFS on top of the nbd device,
> but it can happen with any FS or other modules layered on top of the nbd
> device that can write out data to free memory.  Here a nbd daemon helper
> thread, msgr-worker-1, is performing a write/sendmsg on a socket to execute
> a request. This kicks off a reclaim operation which results in a WRITE to
> the nbd device and the nbd thread calling back into the mm layer.
> 
> [ 1626.609191] msgr-worker-1   D    0  1026      1 0x00004000
> [ 1626.609193] Call Trace:
> [ 1626.609195]  ? __schedule+0x29b/0x630
> [ 1626.609197]  ? wait_for_completion+0xe0/0x170
> [ 1626.609198]  schedule+0x30/0xb0
> [ 1626.609200]  schedule_timeout+0x1f6/0x2f0
> [ 1626.609202]  ? blk_finish_plug+0x21/0x2e
> [ 1626.609204]  ? _xfs_buf_ioapply+0x2e6/0x410
> [ 1626.609206]  ? wait_for_completion+0xe0/0x170
> [ 1626.609208]  wait_for_completion+0x108/0x170
> [ 1626.609210]  ? wake_up_q+0x70/0x70
> [ 1626.609212]  ? __xfs_buf_submit+0x12e/0x250
> [ 1626.609214]  ? xfs_bwrite+0x25/0x60
> [ 1626.609215]  xfs_buf_iowait+0x22/0xf0
> [ 1626.609218]  __xfs_buf_submit+0x12e/0x250
> [ 1626.609220]  xfs_bwrite+0x25/0x60
> [ 1626.609222]  xfs_reclaim_inode+0x2e8/0x310
> [ 1626.609224]  xfs_reclaim_inodes_ag+0x1b6/0x300
> [ 1626.609227]  xfs_reclaim_inodes_nr+0x31/0x40
> [ 1626.609228]  super_cache_scan+0x152/0x1a0
> [ 1626.609231]  do_shrink_slab+0x12c/0x2d0
> [ 1626.609233]  shrink_slab+0x9c/0x2a0
> [ 1626.609235]  shrink_node+0xd7/0x470
> [ 1626.609237]  do_try_to_free_pages+0xbf/0x380
> [ 1626.609240]  try_to_free_pages+0xd9/0x1f0
> [ 1626.609245]  __alloc_pages_slowpath+0x3a4/0xd30
> [ 1626.609251]  ? ___slab_alloc+0x238/0x560
> [ 1626.609254]  __alloc_pages_nodemask+0x30c/0x350
> [ 1626.609259]  skb_page_frag_refill+0x97/0xd0
> [ 1626.609274]  sk_page_frag_refill+0x1d/0x80
> [ 1626.609279]  tcp_sendmsg_locked+0x2bb/0xdd0
> [ 1626.609304]  tcp_sendmsg+0x27/0x40
> [ 1626.609307]  sock_sendmsg+0x54/0x60
> [ 1626.609308]  ___sys_sendmsg+0x29f/0x320
> [ 1626.609313]  ? sock_poll+0x66/0xb0
> [ 1626.609318]  ? ep_item_poll.isra.15+0x40/0xc0
> [ 1626.609320]  ? ep_send_events_proc+0xe6/0x230
> [ 1626.609322]  ? hrtimer_try_to_cancel+0x54/0xf0
> [ 1626.609324]  ? ep_read_events_proc+0xc0/0xc0
> [ 1626.609326]  ? _raw_write_unlock_irq+0xa/0x20
> [ 1626.609327]  ? ep_scan_ready_list.constprop.19+0x218/0x230
> [ 1626.609329]  ? __hrtimer_init+0xb0/0xb0
> [ 1626.609331]  ? _raw_spin_unlock_irq+0xa/0x20
> [ 1626.609334]  ? ep_poll+0x26c/0x4a0
> [ 1626.609337]  ? tcp_tsq_write.part.54+0xa0/0xa0
> [ 1626.609339]  ? release_sock+0x43/0x90
> [ 1626.609341]  ? _raw_spin_unlock_bh+0xa/0x20
> [ 1626.609342]  __sys_sendmsg+0x47/0x80
> [ 1626.609347]  do_syscall_64+0x5f/0x1c0
> [ 1626.609349]  ? prepare_exit_to_usermode+0x75/0xa0
> [ 1626.609351]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> This patch adds a new prctl command that daemons can use after they have
> done their initial setup, and before they start to do allocations that
> are in the IO path. It sets the PF_MEMALLOC_NOIO and PF_LESS_THROTTLE
> flags so both userspace block and FS threads can use it to avoid the
> allocation recursion and try to prevent from being throttled while
> writing out data to free up memory.
> 
> Signed-off-by: Mike Christie <mchristi@redhat.com>
> ---
> V3 
> - Drop NOFS, set PF_LESS_THROTTLE and rename prctl flag to reflect it
> is more general and can support both FS and block devices. Both fuse
> and block device daemons, nbd and tcmu-runner, have been tested to
> confirm the more restrictive PF_MEMALLOC_NOIO also works for fuse.
> 
> - Use CAP_SYS_RESOURCE instead of admin.
> 
> V2:
> - Use prctl instead of procfs.
> - Add support for NOFS for fuse.
> - Check permissions.
> 
> 
>  include/uapi/linux/capability.h |  1 +
>  include/uapi/linux/prctl.h      |  4 ++++
>  kernel/sys.c                    | 26 ++++++++++++++++++++++++++
>  3 files changed, 31 insertions(+)
> 
> diff --git a/include/uapi/linux/capability.h b/include/uapi/linux/capability.h
> index 240fdb9a60f6..272dc69fa080 100644
> --- a/include/uapi/linux/capability.h
> +++ b/include/uapi/linux/capability.h
> @@ -301,6 +301,7 @@ struct vfs_ns_cap_data {
>  /* Allow more than 64hz interrupts from the real-time clock */
>  /* Override max number of consoles on console allocation */
>  /* Override max number of keymaps */
> +/* Control memory reclaim behavior */
>  
>  #define CAP_SYS_RESOURCE     24
>  
> diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
> index 7da1b37b27aa..07b4f8131e36 100644
> --- a/include/uapi/linux/prctl.h
> +++ b/include/uapi/linux/prctl.h
> @@ -234,4 +234,8 @@ struct prctl_mm_map {
>  #define PR_GET_TAGGED_ADDR_CTRL		56
>  # define PR_TAGGED_ADDR_ENABLE		(1UL << 0)
>  
> +/* Control reclaim behavior when allocating memory */
> +#define PR_SET_IO_FLUSHER		57
> +#define PR_GET_IO_FLUSHER		58
> +
>  #endif /* _LINUX_PRCTL_H */
> diff --git a/kernel/sys.c b/kernel/sys.c
> index a611d1d58c7d..08c6b682fa99 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -2486,6 +2486,32 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
>  			return -EINVAL;
>  		error = GET_TAGGED_ADDR_CTRL();
>  		break;
> +	case PR_SET_IO_FLUSHER:
> +		if (!capable(CAP_SYS_RESOURCE))
> +			return -EPERM;
> +
> +		if (arg3 || arg4 || arg5)
> +			return -EINVAL;
> +
> +		if (arg2 == 1)
> +			current->flags |= PF_MEMALLOC_NOIO | PF_LESS_THROTTLE;
> +		else if (!arg2)
> +			current->flags &= ~(PF_MEMALLOC_NOIO | PF_LESS_THROTTLE);
> +		else
> +			return -EINVAL;
> +		break;
> +	case PR_GET_IO_FLUSHER:
> +		if (!capable(CAP_SYS_RESOURCE))
> +			return -EPERM;
> +
> +		if (arg2 || arg3 || arg4 || arg5)
> +			return -EINVAL;
> +
> +		if (current->flags & (PF_MEMALLOC_NOIO | PF_LESS_THROTTLE))
> +			error = 1;
> +		else
> +			error = 0;
> +		break;
>  	default:
>  		error = -EINVAL;
>  		break;
> 

Masato Suzuki in my team tested this with tcmu-runner ZBC file handler.
It solves the memory reclaim recursion deadlock that we have been
observing when this patch is used together with the one I sent yesterday
to the SCSI list (target: core: Prevent memory reclaim recursion).

Sending tested-by tag on behalf of Masato.

Tested-by: Masato Suzuki <masato.suzuki@wdc.com>
Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>


-- 
Damien Le Moal
Western Digital Research


^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [PATCH] Add prctl support for controlling mem reclaim V3
  2019-11-08 18:53 [PATCH] Add prctl support for controlling mem reclaim V3 Mike Christie
  2019-11-09  2:09 ` Damien Le Moal
@ 2019-11-09 19:47 ` Ilya Dryomov
  2019-11-11 15:34   ` Michael Christie
  2019-11-11  9:32 ` Michal Hocko
  2 siblings, 1 reply; 5+ messages in thread
From: Ilya Dryomov @ 2019-11-09 19:47 UTC (permalink / raw)
  To: Mike Christie
  Cc: Michal Hocko, Dave Chinner, linux-mm, LKML, linux-scsi,
	linux-fsdevel, linux-block, martin, Damien.LeMoal

On Fri, Nov 8, 2019 at 8:24 PM Mike Christie <mchristi@redhat.com> wrote:
>
> There are several storage drivers like dm-multipath, iscsi, tcmu-runner,
> amd nbd that have userspace components that can run in the IO path. For
> example, iscsi and nbd's userspace deamons may need to recreate a socket
> and/or send IO on it, and dm-multipath's daemon multipathd may need to
> send SG IO or read/write IO to figure out the state of paths and re-set
> them up.
>
> In the kernel these drivers have access to GFP_NOIO/GFP_NOFS and the
> memalloc_*_save/restore functions to control the allocation behavior,
> but for userspace we would end up hitting an allocation that ended up
> writing data back to the same device we are trying to allocate for.
> The device is then in a state of deadlock, because to execute IO the
> device needs to allocate memory, but to allocate memory the memory
> layers want execute IO to the device.
>
> Here is an example with nbd using a local userspace daemon that performs
> network IO to a remote server. We are using XFS on top of the nbd device,
> but it can happen with any FS or other modules layered on top of the nbd
> device that can write out data to free memory.  Here a nbd daemon helper
> thread, msgr-worker-1, is performing a write/sendmsg on a socket to execute
> a request. This kicks off a reclaim operation which results in a WRITE to
> the nbd device and the nbd thread calling back into the mm layer.
>
> [ 1626.609191] msgr-worker-1   D    0  1026      1 0x00004000
> [ 1626.609193] Call Trace:
> [ 1626.609195]  ? __schedule+0x29b/0x630
> [ 1626.609197]  ? wait_for_completion+0xe0/0x170
> [ 1626.609198]  schedule+0x30/0xb0
> [ 1626.609200]  schedule_timeout+0x1f6/0x2f0
> [ 1626.609202]  ? blk_finish_plug+0x21/0x2e
> [ 1626.609204]  ? _xfs_buf_ioapply+0x2e6/0x410
> [ 1626.609206]  ? wait_for_completion+0xe0/0x170
> [ 1626.609208]  wait_for_completion+0x108/0x170
> [ 1626.609210]  ? wake_up_q+0x70/0x70
> [ 1626.609212]  ? __xfs_buf_submit+0x12e/0x250
> [ 1626.609214]  ? xfs_bwrite+0x25/0x60
> [ 1626.609215]  xfs_buf_iowait+0x22/0xf0
> [ 1626.609218]  __xfs_buf_submit+0x12e/0x250
> [ 1626.609220]  xfs_bwrite+0x25/0x60
> [ 1626.609222]  xfs_reclaim_inode+0x2e8/0x310
> [ 1626.609224]  xfs_reclaim_inodes_ag+0x1b6/0x300
> [ 1626.609227]  xfs_reclaim_inodes_nr+0x31/0x40
> [ 1626.609228]  super_cache_scan+0x152/0x1a0
> [ 1626.609231]  do_shrink_slab+0x12c/0x2d0
> [ 1626.609233]  shrink_slab+0x9c/0x2a0
> [ 1626.609235]  shrink_node+0xd7/0x470
> [ 1626.609237]  do_try_to_free_pages+0xbf/0x380
> [ 1626.609240]  try_to_free_pages+0xd9/0x1f0
> [ 1626.609245]  __alloc_pages_slowpath+0x3a4/0xd30
> [ 1626.609251]  ? ___slab_alloc+0x238/0x560
> [ 1626.609254]  __alloc_pages_nodemask+0x30c/0x350
> [ 1626.609259]  skb_page_frag_refill+0x97/0xd0
> [ 1626.609274]  sk_page_frag_refill+0x1d/0x80
> [ 1626.609279]  tcp_sendmsg_locked+0x2bb/0xdd0
> [ 1626.609304]  tcp_sendmsg+0x27/0x40
> [ 1626.609307]  sock_sendmsg+0x54/0x60
> [ 1626.609308]  ___sys_sendmsg+0x29f/0x320
> [ 1626.609313]  ? sock_poll+0x66/0xb0
> [ 1626.609318]  ? ep_item_poll.isra.15+0x40/0xc0
> [ 1626.609320]  ? ep_send_events_proc+0xe6/0x230
> [ 1626.609322]  ? hrtimer_try_to_cancel+0x54/0xf0
> [ 1626.609324]  ? ep_read_events_proc+0xc0/0xc0
> [ 1626.609326]  ? _raw_write_unlock_irq+0xa/0x20
> [ 1626.609327]  ? ep_scan_ready_list.constprop.19+0x218/0x230
> [ 1626.609329]  ? __hrtimer_init+0xb0/0xb0
> [ 1626.609331]  ? _raw_spin_unlock_irq+0xa/0x20
> [ 1626.609334]  ? ep_poll+0x26c/0x4a0
> [ 1626.609337]  ? tcp_tsq_write.part.54+0xa0/0xa0
> [ 1626.609339]  ? release_sock+0x43/0x90
> [ 1626.609341]  ? _raw_spin_unlock_bh+0xa/0x20
> [ 1626.609342]  __sys_sendmsg+0x47/0x80
> [ 1626.609347]  do_syscall_64+0x5f/0x1c0
> [ 1626.609349]  ? prepare_exit_to_usermode+0x75/0xa0
> [ 1626.609351]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> This patch adds a new prctl command that daemons can use after they have
> done their initial setup, and before they start to do allocations that
> are in the IO path. It sets the PF_MEMALLOC_NOIO and PF_LESS_THROTTLE
> flags so both userspace block and FS threads can use it to avoid the
> allocation recursion and try to prevent from being throttled while
> writing out data to free up memory.
>
> Signed-off-by: Mike Christie <mchristi@redhat.com>
> ---
> V3
> - Drop NOFS, set PF_LESS_THROTTLE and rename prctl flag to reflect it
> is more general and can support both FS and block devices. Both fuse
> and block device daemons, nbd and tcmu-runner, have been tested to
> confirm the more restrictive PF_MEMALLOC_NOIO also works for fuse.
>
> - Use CAP_SYS_RESOURCE instead of admin.
>
> V2:
> - Use prctl instead of procfs.
> - Add support for NOFS for fuse.
> - Check permissions.
>
>
>  include/uapi/linux/capability.h |  1 +
>  include/uapi/linux/prctl.h      |  4 ++++
>  kernel/sys.c                    | 26 ++++++++++++++++++++++++++
>  3 files changed, 31 insertions(+)
>
> diff --git a/include/uapi/linux/capability.h b/include/uapi/linux/capability.h
> index 240fdb9a60f6..272dc69fa080 100644
> --- a/include/uapi/linux/capability.h
> +++ b/include/uapi/linux/capability.h
> @@ -301,6 +301,7 @@ struct vfs_ns_cap_data {
>  /* Allow more than 64hz interrupts from the real-time clock */
>  /* Override max number of consoles on console allocation */
>  /* Override max number of keymaps */
> +/* Control memory reclaim behavior */
>
>  #define CAP_SYS_RESOURCE     24
>
> diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
> index 7da1b37b27aa..07b4f8131e36 100644
> --- a/include/uapi/linux/prctl.h
> +++ b/include/uapi/linux/prctl.h
> @@ -234,4 +234,8 @@ struct prctl_mm_map {
>  #define PR_GET_TAGGED_ADDR_CTRL                56
>  # define PR_TAGGED_ADDR_ENABLE         (1UL << 0)
>
> +/* Control reclaim behavior when allocating memory */
> +#define PR_SET_IO_FLUSHER              57
> +#define PR_GET_IO_FLUSHER              58
> +
>  #endif /* _LINUX_PRCTL_H */
> diff --git a/kernel/sys.c b/kernel/sys.c
> index a611d1d58c7d..08c6b682fa99 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -2486,6 +2486,32 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
>                         return -EINVAL;
>                 error = GET_TAGGED_ADDR_CTRL();
>                 break;
> +       case PR_SET_IO_FLUSHER:
> +               if (!capable(CAP_SYS_RESOURCE))
> +                       return -EPERM;
> +
> +               if (arg3 || arg4 || arg5)
> +                       return -EINVAL;
> +
> +               if (arg2 == 1)
> +                       current->flags |= PF_MEMALLOC_NOIO | PF_LESS_THROTTLE;
> +               else if (!arg2)
> +                       current->flags &= ~(PF_MEMALLOC_NOIO | PF_LESS_THROTTLE);
> +               else
> +                       return -EINVAL;
> +               break;
> +       case PR_GET_IO_FLUSHER:
> +               if (!capable(CAP_SYS_RESOURCE))
> +                       return -EPERM;
> +
> +               if (arg2 || arg3 || arg4 || arg5)
> +                       return -EINVAL;
> +
> +               if (current->flags & (PF_MEMALLOC_NOIO | PF_LESS_THROTTLE))

I think it needs to be conditioned on both flags instead of just one of
them, for consistency with SET.  Seems worth a define too, PF_IO_FLUSHER?
Or something local to this file at least.

> +                       error = 1;
> +               else
> +                       error = 0;

  error = (current->flags & PF_IO_FLUSHER) == PF_IO_FLUSHER;

Thanks,

                Ilya


^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [PATCH] Add prctl support for controlling mem reclaim V3
  2019-11-08 18:53 [PATCH] Add prctl support for controlling mem reclaim V3 Mike Christie
  2019-11-09  2:09 ` Damien Le Moal
  2019-11-09 19:47 ` Ilya Dryomov
@ 2019-11-11  9:32 ` Michal Hocko
  2 siblings, 0 replies; 5+ messages in thread
From: Michal Hocko @ 2019-11-11  9:32 UTC (permalink / raw)
  To: Mike Christie
  Cc: david, linux-mm, linux-kernel, linux-scsi, linux-fsdevel,
	linux-block, martin, Damien.LeMoal, linux-api

[Cc linux-api]

On Fri 08-11-19 12:53:19, Mike Christie wrote:
> There are several storage drivers like dm-multipath, iscsi, tcmu-runner,
> amd nbd that have userspace components that can run in the IO path. For
> example, iscsi and nbd's userspace deamons may need to recreate a socket
> and/or send IO on it, and dm-multipath's daemon multipathd may need to
> send SG IO or read/write IO to figure out the state of paths and re-set
> them up.
> 
> In the kernel these drivers have access to GFP_NOIO/GFP_NOFS and the
> memalloc_*_save/restore functions to control the allocation behavior,
> but for userspace we would end up hitting an allocation that ended up
> writing data back to the same device we are trying to allocate for.
> The device is then in a state of deadlock, because to execute IO the
> device needs to allocate memory, but to allocate memory the memory
> layers want execute IO to the device.
> 
> Here is an example with nbd using a local userspace daemon that performs
> network IO to a remote server. We are using XFS on top of the nbd device,
> but it can happen with any FS or other modules layered on top of the nbd
> device that can write out data to free memory.  Here a nbd daemon helper
> thread, msgr-worker-1, is performing a write/sendmsg on a socket to execute
> a request. This kicks off a reclaim operation which results in a WRITE to
> the nbd device and the nbd thread calling back into the mm layer.
> 
> [ 1626.609191] msgr-worker-1   D    0  1026      1 0x00004000
> [ 1626.609193] Call Trace:
> [ 1626.609195]  ? __schedule+0x29b/0x630
> [ 1626.609197]  ? wait_for_completion+0xe0/0x170
> [ 1626.609198]  schedule+0x30/0xb0
> [ 1626.609200]  schedule_timeout+0x1f6/0x2f0
> [ 1626.609202]  ? blk_finish_plug+0x21/0x2e
> [ 1626.609204]  ? _xfs_buf_ioapply+0x2e6/0x410
> [ 1626.609206]  ? wait_for_completion+0xe0/0x170
> [ 1626.609208]  wait_for_completion+0x108/0x170
> [ 1626.609210]  ? wake_up_q+0x70/0x70
> [ 1626.609212]  ? __xfs_buf_submit+0x12e/0x250
> [ 1626.609214]  ? xfs_bwrite+0x25/0x60
> [ 1626.609215]  xfs_buf_iowait+0x22/0xf0
> [ 1626.609218]  __xfs_buf_submit+0x12e/0x250
> [ 1626.609220]  xfs_bwrite+0x25/0x60
> [ 1626.609222]  xfs_reclaim_inode+0x2e8/0x310
> [ 1626.609224]  xfs_reclaim_inodes_ag+0x1b6/0x300
> [ 1626.609227]  xfs_reclaim_inodes_nr+0x31/0x40
> [ 1626.609228]  super_cache_scan+0x152/0x1a0
> [ 1626.609231]  do_shrink_slab+0x12c/0x2d0
> [ 1626.609233]  shrink_slab+0x9c/0x2a0
> [ 1626.609235]  shrink_node+0xd7/0x470
> [ 1626.609237]  do_try_to_free_pages+0xbf/0x380
> [ 1626.609240]  try_to_free_pages+0xd9/0x1f0
> [ 1626.609245]  __alloc_pages_slowpath+0x3a4/0xd30
> [ 1626.609251]  ? ___slab_alloc+0x238/0x560
> [ 1626.609254]  __alloc_pages_nodemask+0x30c/0x350
> [ 1626.609259]  skb_page_frag_refill+0x97/0xd0
> [ 1626.609274]  sk_page_frag_refill+0x1d/0x80
> [ 1626.609279]  tcp_sendmsg_locked+0x2bb/0xdd0
> [ 1626.609304]  tcp_sendmsg+0x27/0x40
> [ 1626.609307]  sock_sendmsg+0x54/0x60
> [ 1626.609308]  ___sys_sendmsg+0x29f/0x320
> [ 1626.609313]  ? sock_poll+0x66/0xb0
> [ 1626.609318]  ? ep_item_poll.isra.15+0x40/0xc0
> [ 1626.609320]  ? ep_send_events_proc+0xe6/0x230
> [ 1626.609322]  ? hrtimer_try_to_cancel+0x54/0xf0
> [ 1626.609324]  ? ep_read_events_proc+0xc0/0xc0
> [ 1626.609326]  ? _raw_write_unlock_irq+0xa/0x20
> [ 1626.609327]  ? ep_scan_ready_list.constprop.19+0x218/0x230
> [ 1626.609329]  ? __hrtimer_init+0xb0/0xb0
> [ 1626.609331]  ? _raw_spin_unlock_irq+0xa/0x20
> [ 1626.609334]  ? ep_poll+0x26c/0x4a0
> [ 1626.609337]  ? tcp_tsq_write.part.54+0xa0/0xa0
> [ 1626.609339]  ? release_sock+0x43/0x90
> [ 1626.609341]  ? _raw_spin_unlock_bh+0xa/0x20
> [ 1626.609342]  __sys_sendmsg+0x47/0x80
> [ 1626.609347]  do_syscall_64+0x5f/0x1c0
> [ 1626.609349]  ? prepare_exit_to_usermode+0x75/0xa0
> [ 1626.609351]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> This patch adds a new prctl command that daemons can use after they have
> done their initial setup, and before they start to do allocations that
> are in the IO path. It sets the PF_MEMALLOC_NOIO and PF_LESS_THROTTLE
> flags so both userspace block and FS threads can use it to avoid the
> allocation recursion and try to prevent from being throttled while
> writing out data to free up memory.
> 
> Signed-off-by: Mike Christie <mchristi@redhat.com>

OK, this looks much better then explicitly exposing NOIO/NOFS to the
userspace. Restricting to CAP_SYS_RESOURCE makes sense as well but I am
not really an expert in that direction.

So for the proposed semantic this makes sense
Acked-by: Michal Hocko <mhocko@suse.com>

Please do not forget to add a man page update.

Keeping the rest of the email for the new CC

> ---
> V3 
> - Drop NOFS, set PF_LESS_THROTTLE and rename prctl flag to reflect it
> is more general and can support both FS and block devices. Both fuse
> and block device daemons, nbd and tcmu-runner, have been tested to
> confirm the more restrictive PF_MEMALLOC_NOIO also works for fuse.
> 
> - Use CAP_SYS_RESOURCE instead of admin.
> 
> V2:
> - Use prctl instead of procfs.
> - Add support for NOFS for fuse.
> - Check permissions.
> 
> 
>  include/uapi/linux/capability.h |  1 +
>  include/uapi/linux/prctl.h      |  4 ++++
>  kernel/sys.c                    | 26 ++++++++++++++++++++++++++
>  3 files changed, 31 insertions(+)
> 
> diff --git a/include/uapi/linux/capability.h b/include/uapi/linux/capability.h
> index 240fdb9a60f6..272dc69fa080 100644
> --- a/include/uapi/linux/capability.h
> +++ b/include/uapi/linux/capability.h
> @@ -301,6 +301,7 @@ struct vfs_ns_cap_data {
>  /* Allow more than 64hz interrupts from the real-time clock */
>  /* Override max number of consoles on console allocation */
>  /* Override max number of keymaps */
> +/* Control memory reclaim behavior */
>  
>  #define CAP_SYS_RESOURCE     24
>  
> diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
> index 7da1b37b27aa..07b4f8131e36 100644
> --- a/include/uapi/linux/prctl.h
> +++ b/include/uapi/linux/prctl.h
> @@ -234,4 +234,8 @@ struct prctl_mm_map {
>  #define PR_GET_TAGGED_ADDR_CTRL		56
>  # define PR_TAGGED_ADDR_ENABLE		(1UL << 0)
>  
> +/* Control reclaim behavior when allocating memory */
> +#define PR_SET_IO_FLUSHER		57
> +#define PR_GET_IO_FLUSHER		58
> +
>  #endif /* _LINUX_PRCTL_H */
> diff --git a/kernel/sys.c b/kernel/sys.c
> index a611d1d58c7d..08c6b682fa99 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -2486,6 +2486,32 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
>  			return -EINVAL;
>  		error = GET_TAGGED_ADDR_CTRL();
>  		break;
> +	case PR_SET_IO_FLUSHER:
> +		if (!capable(CAP_SYS_RESOURCE))
> +			return -EPERM;
> +
> +		if (arg3 || arg4 || arg5)
> +			return -EINVAL;
> +
> +		if (arg2 == 1)
> +			current->flags |= PF_MEMALLOC_NOIO | PF_LESS_THROTTLE;
> +		else if (!arg2)
> +			current->flags &= ~(PF_MEMALLOC_NOIO | PF_LESS_THROTTLE);
> +		else
> +			return -EINVAL;
> +		break;
> +	case PR_GET_IO_FLUSHER:
> +		if (!capable(CAP_SYS_RESOURCE))
> +			return -EPERM;
> +
> +		if (arg2 || arg3 || arg4 || arg5)
> +			return -EINVAL;
> +
> +		if (current->flags & (PF_MEMALLOC_NOIO | PF_LESS_THROTTLE))
> +			error = 1;
> +		else
> +			error = 0;
> +		break;
>  	default:
>  		error = -EINVAL;
>  		break;
> -- 
> 2.20.1
> 

-- 
Michal Hocko
SUSE Labs


^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [PATCH] Add prctl support for controlling mem reclaim V3
  2019-11-09 19:47 ` Ilya Dryomov
@ 2019-11-11 15:34   ` Michael Christie
  0 siblings, 0 replies; 5+ messages in thread
From: Michael Christie @ 2019-11-11 15:34 UTC (permalink / raw)
  To: Ilya Dryomov
  Cc: Michal Hocko, Dave Chinner, linux-mm, LKML, linux-scsi,
	linux-fsdevel, linux-block, martin, Damien.LeMoal

On 11/09/2019 01:47 PM, Ilya Dryomov wrote:
> On Fri, Nov 8, 2019 at 8:24 PM Mike Christie <mchristi@redhat.com> wrote:
>>
>> There are several storage drivers like dm-multipath, iscsi, tcmu-runner,
>> amd nbd that have userspace components that can run in the IO path. For
>> example, iscsi and nbd's userspace deamons may need to recreate a socket
>> and/or send IO on it, and dm-multipath's daemon multipathd may need to
>> send SG IO or read/write IO to figure out the state of paths and re-set
>> them up.
>>
>> In the kernel these drivers have access to GFP_NOIO/GFP_NOFS and the
>> memalloc_*_save/restore functions to control the allocation behavior,
>> but for userspace we would end up hitting an allocation that ended up
>> writing data back to the same device we are trying to allocate for.
>> The device is then in a state of deadlock, because to execute IO the
>> device needs to allocate memory, but to allocate memory the memory
>> layers want execute IO to the device.
>>
>> Here is an example with nbd using a local userspace daemon that performs
>> network IO to a remote server. We are using XFS on top of the nbd device,
>> but it can happen with any FS or other modules layered on top of the nbd
>> device that can write out data to free memory.  Here a nbd daemon helper
>> thread, msgr-worker-1, is performing a write/sendmsg on a socket to execute
>> a request. This kicks off a reclaim operation which results in a WRITE to
>> the nbd device and the nbd thread calling back into the mm layer.
>>
>> [ 1626.609191] msgr-worker-1   D    0  1026      1 0x00004000
>> [ 1626.609193] Call Trace:
>> [ 1626.609195]  ? __schedule+0x29b/0x630
>> [ 1626.609197]  ? wait_for_completion+0xe0/0x170
>> [ 1626.609198]  schedule+0x30/0xb0
>> [ 1626.609200]  schedule_timeout+0x1f6/0x2f0
>> [ 1626.609202]  ? blk_finish_plug+0x21/0x2e
>> [ 1626.609204]  ? _xfs_buf_ioapply+0x2e6/0x410
>> [ 1626.609206]  ? wait_for_completion+0xe0/0x170
>> [ 1626.609208]  wait_for_completion+0x108/0x170
>> [ 1626.609210]  ? wake_up_q+0x70/0x70
>> [ 1626.609212]  ? __xfs_buf_submit+0x12e/0x250
>> [ 1626.609214]  ? xfs_bwrite+0x25/0x60
>> [ 1626.609215]  xfs_buf_iowait+0x22/0xf0
>> [ 1626.609218]  __xfs_buf_submit+0x12e/0x250
>> [ 1626.609220]  xfs_bwrite+0x25/0x60
>> [ 1626.609222]  xfs_reclaim_inode+0x2e8/0x310
>> [ 1626.609224]  xfs_reclaim_inodes_ag+0x1b6/0x300
>> [ 1626.609227]  xfs_reclaim_inodes_nr+0x31/0x40
>> [ 1626.609228]  super_cache_scan+0x152/0x1a0
>> [ 1626.609231]  do_shrink_slab+0x12c/0x2d0
>> [ 1626.609233]  shrink_slab+0x9c/0x2a0
>> [ 1626.609235]  shrink_node+0xd7/0x470
>> [ 1626.609237]  do_try_to_free_pages+0xbf/0x380
>> [ 1626.609240]  try_to_free_pages+0xd9/0x1f0
>> [ 1626.609245]  __alloc_pages_slowpath+0x3a4/0xd30
>> [ 1626.609251]  ? ___slab_alloc+0x238/0x560
>> [ 1626.609254]  __alloc_pages_nodemask+0x30c/0x350
>> [ 1626.609259]  skb_page_frag_refill+0x97/0xd0
>> [ 1626.609274]  sk_page_frag_refill+0x1d/0x80
>> [ 1626.609279]  tcp_sendmsg_locked+0x2bb/0xdd0
>> [ 1626.609304]  tcp_sendmsg+0x27/0x40
>> [ 1626.609307]  sock_sendmsg+0x54/0x60
>> [ 1626.609308]  ___sys_sendmsg+0x29f/0x320
>> [ 1626.609313]  ? sock_poll+0x66/0xb0
>> [ 1626.609318]  ? ep_item_poll.isra.15+0x40/0xc0
>> [ 1626.609320]  ? ep_send_events_proc+0xe6/0x230
>> [ 1626.609322]  ? hrtimer_try_to_cancel+0x54/0xf0
>> [ 1626.609324]  ? ep_read_events_proc+0xc0/0xc0
>> [ 1626.609326]  ? _raw_write_unlock_irq+0xa/0x20
>> [ 1626.609327]  ? ep_scan_ready_list.constprop.19+0x218/0x230
>> [ 1626.609329]  ? __hrtimer_init+0xb0/0xb0
>> [ 1626.609331]  ? _raw_spin_unlock_irq+0xa/0x20
>> [ 1626.609334]  ? ep_poll+0x26c/0x4a0
>> [ 1626.609337]  ? tcp_tsq_write.part.54+0xa0/0xa0
>> [ 1626.609339]  ? release_sock+0x43/0x90
>> [ 1626.609341]  ? _raw_spin_unlock_bh+0xa/0x20
>> [ 1626.609342]  __sys_sendmsg+0x47/0x80
>> [ 1626.609347]  do_syscall_64+0x5f/0x1c0
>> [ 1626.609349]  ? prepare_exit_to_usermode+0x75/0xa0
>> [ 1626.609351]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
>>
>> This patch adds a new prctl command that daemons can use after they have
>> done their initial setup, and before they start to do allocations that
>> are in the IO path. It sets the PF_MEMALLOC_NOIO and PF_LESS_THROTTLE
>> flags so both userspace block and FS threads can use it to avoid the
>> allocation recursion and try to prevent from being throttled while
>> writing out data to free up memory.
>>
>> Signed-off-by: Mike Christie <mchristi@redhat.com>
>> ---
>> V3
>> - Drop NOFS, set PF_LESS_THROTTLE and rename prctl flag to reflect it
>> is more general and can support both FS and block devices. Both fuse
>> and block device daemons, nbd and tcmu-runner, have been tested to
>> confirm the more restrictive PF_MEMALLOC_NOIO also works for fuse.
>>
>> - Use CAP_SYS_RESOURCE instead of admin.
>>
>> V2:
>> - Use prctl instead of procfs.
>> - Add support for NOFS for fuse.
>> - Check permissions.
>>
>>
>>  include/uapi/linux/capability.h |  1 +
>>  include/uapi/linux/prctl.h      |  4 ++++
>>  kernel/sys.c                    | 26 ++++++++++++++++++++++++++
>>  3 files changed, 31 insertions(+)
>>
>> diff --git a/include/uapi/linux/capability.h b/include/uapi/linux/capability.h
>> index 240fdb9a60f6..272dc69fa080 100644
>> --- a/include/uapi/linux/capability.h
>> +++ b/include/uapi/linux/capability.h
>> @@ -301,6 +301,7 @@ struct vfs_ns_cap_data {
>>  /* Allow more than 64hz interrupts from the real-time clock */
>>  /* Override max number of consoles on console allocation */
>>  /* Override max number of keymaps */
>> +/* Control memory reclaim behavior */
>>
>>  #define CAP_SYS_RESOURCE     24
>>
>> diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
>> index 7da1b37b27aa..07b4f8131e36 100644
>> --- a/include/uapi/linux/prctl.h
>> +++ b/include/uapi/linux/prctl.h
>> @@ -234,4 +234,8 @@ struct prctl_mm_map {
>>  #define PR_GET_TAGGED_ADDR_CTRL                56
>>  # define PR_TAGGED_ADDR_ENABLE         (1UL << 0)
>>
>> +/* Control reclaim behavior when allocating memory */
>> +#define PR_SET_IO_FLUSHER              57
>> +#define PR_GET_IO_FLUSHER              58
>> +
>>  #endif /* _LINUX_PRCTL_H */
>> diff --git a/kernel/sys.c b/kernel/sys.c
>> index a611d1d58c7d..08c6b682fa99 100644
>> --- a/kernel/sys.c
>> +++ b/kernel/sys.c
>> @@ -2486,6 +2486,32 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
>>                         return -EINVAL;
>>                 error = GET_TAGGED_ADDR_CTRL();
>>                 break;
>> +       case PR_SET_IO_FLUSHER:
>> +               if (!capable(CAP_SYS_RESOURCE))
>> +                       return -EPERM;
>> +
>> +               if (arg3 || arg4 || arg5)
>> +                       return -EINVAL;
>> +
>> +               if (arg2 == 1)
>> +                       current->flags |= PF_MEMALLOC_NOIO | PF_LESS_THROTTLE;
>> +               else if (!arg2)
>> +                       current->flags &= ~(PF_MEMALLOC_NOIO | PF_LESS_THROTTLE);
>> +               else
>> +                       return -EINVAL;
>> +               break;
>> +       case PR_GET_IO_FLUSHER:
>> +               if (!capable(CAP_SYS_RESOURCE))
>> +                       return -EPERM;
>> +
>> +               if (arg2 || arg3 || arg4 || arg5)
>> +                       return -EINVAL;
>> +
>> +               if (current->flags & (PF_MEMALLOC_NOIO | PF_LESS_THROTTLE))
> 
> I think it needs to be conditioned on both flags instead of just one of
> them, for consistency with SET.  Seems worth a define too, PF_IO_FLUSHER?
> Or something local to this file at least.

Yeah, that was a mistake. Will fix.

> 
>> +                       error = 1;
>> +               else
>> +                       error = 0;
> 
>   error = (current->flags & PF_IO_FLUSHER) == PF_IO_FLUSHER;
> 
> Thanks,
> 
>                 Ilya
> 



^ permalink raw reply	[flat|nested] 5+ messages in thread

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Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-11-08 18:53 [PATCH] Add prctl support for controlling mem reclaim V3 Mike Christie
2019-11-09  2:09 ` Damien Le Moal
2019-11-09 19:47 ` Ilya Dryomov
2019-11-11 15:34   ` Michael Christie
2019-11-11  9:32 ` Michal Hocko

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