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Date: Thu, 3 Dec 2015 21:43:13 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Tejun Heo <tj@kernel.org>
Cc: Ulrich Obergfell <uobergfe@redhat.com>, Ingo Molnar <mingo@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, kernel-team@fb.com
Subject: Re: [PATCH] workqueue: warn if memory reclaim tries to flush
 !WQ_MEM_RECLAIM workqueue
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On Thu, Dec 03, 2015 at 02:26:16PM -0500, Tejun Heo wrote:
> +	WARN_ONCE(current->flags & PF_MEMALLOC,

I'm not sure about using PF_MEMALLOC for detecting reclaim. There appear
to be more sites setting this than reclaim. See:

drivers/block/nbd.c:	current->flags |= PF_MEMALLOC;
drivers/mmc/card/queue.c:	current->flags |= PF_MEMALLOC;
drivers/mtd/nand/nandsim.c:	current->flags |= PF_MEMALLOC;
drivers/scsi/iscsi_tcp.c:	current->flags |= PF_MEMALLOC;
drivers/staging/lustre/include/linux/libcfs/linux/linux-mem.h:#define memory_pressure_set() do { current->flags |= PF_MEMALLOC; } while (0)
fs/cifs/connect.c:	current->flags |= PF_MEMALLOC;
fs/xfs/libxfs/xfs_btree.c:		new_pflags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
fs/xfs/xfs_trans_ail.c:	current->flags |= PF_MEMALLOC;
include/linux/sched.h:	current->flags |= PF_MEMALLOC_NOIO;
mm/page_alloc.c:	current->flags |= PF_MEMALLOC;
mm/page_alloc.c:	current->flags |= PF_MEMALLOC;
mm/vmscan.c:	tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
mm/vmscan.c:	p->flags |= PF_MEMALLOC;
mm/vmscan.c:	p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
net/core/dev.c:		current->flags |= PF_MEMALLOC;
net/core/sock.c:	current->flags |= PF_MEMALLOC;


The actual reclaim sites in page_alloc and vmscan set
current->reclaim_state. So testing against that might be more accurate.