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Commit 9fd2c02a authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Vinayak Menon
Browse files

mm: turn vmap_purge_lock into a mutex 

The purge_lock spinlock causes high latencies with non RT kernel.  This
has been reported multiple times on lkml [1] [2] and affects
applications like audio.

This patch replaces it with a mutex to allow preemption while holding
the lock.

Thanks to Joel Fernandes for the detailed report and analysis as well as
an earlier attempt at fixing this issue.

[1] http://lists.openwall.net/linux-kernel/2016/03/23/29
[2] https://lkml.org/lkml/2016/10/9/59

Change-Id: I57d4e9c7ce5aeb3273574026da2a8b737ef0b809
Link: http://lkml.kernel.org/r/1479474236-4139-10-git-send-email-hch@lst.de


Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Tested-by: default avatarJisheng Zhang <jszhang@marvell.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Joel Fernandes <joelaf@google.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: John Dias <joaodias@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Git-commit: f9e09977671b618aeb25ddc0d4c9a84d5b5cde9d
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: default avatarVinayak Menon <vinmenon@codeaurora.org>
parent 4a4394c3

mm/vmalloc.c

+7 −7
Original line number Diff line number Diff line
@@ -667,7 +667,7 @@ static atomic_t vmap_lazy_nr = ATOMIC_INIT(0); 
 * by this look, but we want to avoid concurrent calls for performance

 * reasons and to make the pcpu_get_vm_areas more deterministic.

 */

static DEFINE_SPINLOCK(vmap_purge_lock);

static DEFINE_MUTEX(vmap_purge_lock);



/* for per-CPU blocks */

static void purge_fragmented_blocks_allcpus(void);
@@ -721,9 +721,9 @@ static bool __purge_vmap_area_lazy(unsigned long start, unsigned long end) 
 */

static void try_purge_vmap_area_lazy(void)

{

	if (spin_trylock(&vmap_purge_lock)) {

	if (mutex_trylock(&vmap_purge_lock)) {

		__purge_vmap_area_lazy(ULONG_MAX, 0);

		spin_unlock(&vmap_purge_lock);

		mutex_unlock(&vmap_purge_lock);

	}

}
@@ -732,10 +732,10 @@ static void try_purge_vmap_area_lazy(void) 
 */

static void purge_vmap_area_lazy(void)

{

	spin_lock(&vmap_purge_lock);

	mutex_lock(&vmap_purge_lock);

	purge_fragmented_blocks_allcpus();

	__purge_vmap_area_lazy(ULONG_MAX, 0);

	spin_unlock(&vmap_purge_lock);

	mutex_unlock(&vmap_purge_lock);

}



/*
@@ -1124,11 +1124,11 @@ void vm_unmap_aliases(void) 
		rcu_read_unlock();

	}



	spin_lock(&vmap_purge_lock);

	mutex_lock(&vmap_purge_lock);

	purge_fragmented_blocks_allcpus();

	if (!__purge_vmap_area_lazy(start, end) && flush)

		flush_tlb_kernel_range(start, end);

	spin_unlock(&vmap_purge_lock);

	mutex_unlock(&vmap_purge_lock);

}

EXPORT_SYMBOL_GPL(vm_unmap_aliases);