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Commit 2a8a9867 authored by Mauricio Faria de Oliveira's avatar Mauricio Faria de Oliveira Committed by Benjamin LaHaise
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fs: aio: fix the increment of aio-nr and counting against aio-max-nr 



Currently, aio-nr is incremented in steps of 'num_possible_cpus() * 8'
for io_setup(nr_events, ..) with 'nr_events < num_possible_cpus() * 4':

    ioctx_alloc()
    ...
        nr_events = max(nr_events, num_possible_cpus() * 4);
        nr_events *= 2;
    ...
        ctx->max_reqs = nr_events;
    ...
        aio_nr += ctx->max_reqs;
    ....

This limits the number of aio contexts actually available to much less
than aio-max-nr, and is increasingly worse with greater number of CPUs.

For example, with 64 CPUs, only 256 aio contexts are actually available
(with aio-max-nr = 65536) because the increment is 512 in that scenario.

Note: 65536 [max aio contexts] / (64*4*2) [increment per aio context]
is 128, but make it 256 (double) as counting against 'aio-max-nr * 2':

    ioctx_alloc()
    ...
        if (aio_nr + nr_events > (aio_max_nr * 2UL) ||
        ...
            goto err_ctx;
    ...

This patch uses the original value of nr_events (from userspace) to
increment aio-nr and count against aio-max-nr, which resolves those.

Signed-off-by: default avatarMauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>
Reported-by: default avatarLekshmi C. Pillai <lekshmi.cpillai@in.ibm.com>
Tested-by: default avatarLekshmi C. Pillai <lekshmi.cpillai@in.ibm.com>
Tested-by: default avatarPaul Nguyen <nguyenp@us.ibm.com>
Reviewed-by: default avatarJeff Moyer <jmoyer@redhat.com>
Signed-off-by: default avatarBenjamin LaHaise <bcrl@kvack.org>
parent 569dbb88

fs/aio.c

+12 −7
Original line number Diff line number Diff line
@@ -441,10 +441,9 @@ static const struct address_space_operations aio_ctx_aops = { 
#endif

};



static int aio_setup_ring(struct kioctx *ctx)

static int aio_setup_ring(struct kioctx *ctx, unsigned int nr_events)

{

	struct aio_ring *ring;

	unsigned nr_events = ctx->max_reqs;

	struct mm_struct *mm = current->mm;

	unsigned long size, unused;

	int nr_pages;
@@ -706,6 +705,12 @@ static struct kioctx *ioctx_alloc(unsigned nr_events) 
	struct kioctx *ctx;

	int err = -ENOMEM;



	/*

	 * Store the original nr_events -- what userspace passed to io_setup(),

	 * for counting against the global limit -- before it changes.

	 */

	unsigned int max_reqs = nr_events;



	/*

	 * We keep track of the number of available ringbuffer slots, to prevent

	 * overflow (reqs_available), and we also use percpu counters for this.
@@ -724,14 +729,14 @@ static struct kioctx *ioctx_alloc(unsigned nr_events) 
		return ERR_PTR(-EINVAL);

	}



	if (!nr_events || (unsigned long)nr_events > (aio_max_nr * 2UL))

	if (!nr_events || (unsigned long)max_reqs > aio_max_nr)

		return ERR_PTR(-EAGAIN);



	ctx = kmem_cache_zalloc(kioctx_cachep, GFP_KERNEL);

	if (!ctx)

		return ERR_PTR(-ENOMEM);



	ctx->max_reqs = nr_events;

	ctx->max_reqs = max_reqs;



	spin_lock_init(&ctx->ctx_lock);

	spin_lock_init(&ctx->completion_lock);
@@ -753,7 +758,7 @@ static struct kioctx *ioctx_alloc(unsigned nr_events) 
	if (!ctx->cpu)

		goto err;



	err = aio_setup_ring(ctx);

	err = aio_setup_ring(ctx, nr_events);

	if (err < 0)

		goto err;
@@ -764,8 +769,8 @@ static struct kioctx *ioctx_alloc(unsigned nr_events) 


	/* limit the number of system wide aios */

	spin_lock(&aio_nr_lock);

	if (aio_nr + nr_events > (aio_max_nr * 2UL) ||

	    aio_nr + nr_events < aio_nr) {

	if (aio_nr + ctx->max_reqs > aio_max_nr ||

	    aio_nr + ctx->max_reqs < aio_nr) {

		spin_unlock(&aio_nr_lock);

		err = -EAGAIN;

		goto err_ctx;