@@ -441,10 +441,9 @@ static int aio_migratepage(struct address_space *mapping, struct page *new,
#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;
@@ -707,6 +706,12 @@ static struct kioctx *ioctx_alloc(unsigned nr_events)
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;
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] / (2*4*64) [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. The test-case and test-suite validation steps are included later in this patch message, for documentation purposes. Example on a system with 64 CPUs: # cat /sys/devices/system/cpu/possible 0-63 # grep . /proc/sys/fs/aio-* /proc/sys/fs/aio-max-nr:65536 /proc/sys/fs/aio-nr:0 test 1) number of aio contexts available with nr_events == 1 ------------------------------------------------------------- This test calls io_setup(1, ..) up to 65536 times, exiting on error. - original kernel: Only 256 aio contexts could be created successfully, quickly falling into the aio-max-nr exceeded error path (-EAGAIN). # ./io_setup 1 65536 | grep -m1 . - /proc/sys/fs/aio-nr (standard input):io_setup(1, ): 256 calls with rc 0, last call with rc -11. /proc/sys/fs/aio-nr:131072 One might notice the aio-nr value is twice the aio-max-nr limit, an effect of how the current code handles that 'nr_events *= 2'. - patched kernel: Almost all of the limit of aio contexts could be allocated, eventually falling into the insufficient resources error path (-ENOMEM): # ./io_setup 1 65536 | grep -m1 . - /proc/sys/fs/aio-nr (standard input):io_setup(1, ): 65516 calls with rc 0, last call with rc -12. /proc/sys/fs/aio-nr:65516 Notice the aio-nr value is now _under_ the aio-max-nr limit. test 2) increment value for nr_events == 1 ------------------------------------------- This test calls io_setup(1, ..) only 1 time, to show the increment: - original kernel: # ./io_setup 1 1 | grep -m1 . - /proc/sys/fs/aio-nr (standard input):io_setup(1, ) : 1 calls with rc 0, last call with rc 0. /proc/sys/fs/aio-nr:512 Notice the increment is 'num_online_cpus() * 8'. - patched kernel: # ./io_setup 1 1 | grep -m1 . - /proc/sys/fs/aio-nr (standard input):io_setup(1, ): 1 calls with rc 0, last call with rc 0. /proc/sys/fs/aio-nr:1 Notice the increment is exactly 1 (matches nr_events from userspace). test 3) more aio contexts available with great-enough nr_events ---------------------------------------------------------------- The full aio-max-nr limit (65536) is available for greater nr_events. This test calls io_setup(1024, ) exactly 64 times, without error. - original kernel: # ./io_setup 1024 64 | grep -m1 . - /proc/sys/fs/aio-nr (standard input):io_setup(1024, ): 64 calls with rc 0, last call with rc 0. /proc/sys/fs/aio-nr:131072 Notice the aio-nr value is twice the aio-max-nr limit. - patched kernel: # ./io_setup 1024 64 | grep -m1 . - /proc/sys/fs/aio-nr (standard input):io_setup(1024, ): 64 calls with rc 0, last call with rc 0. /proc/sys/fs/aio-nr:65536 Notice the aio-nr value is now _exactly_ the aio-max-nr limit. Test-case: io_setup.c # gcc -o io_setup io_setup.c -laio """ #include <libaio.h> #include <stdio.h> #include <stdlib.h> #include <unistd.h> int main(int argc, char *argv[]) { int nr_events, nr_calls, rc, i; io_context_t *ioctx; /* usage: io_setup <nr_events for io_setup()> <max calls to io_setup()> */ if (argc != 3) return -1; nr_events = atoi(argv[1]); nr_calls = atoi(argv[2]); ioctx = calloc(nr_calls, sizeof(*ioctx)); if (!ioctx) return -2; for (i = 0; i < nr_calls; i++) if (rc = io_setup(nr_events, &ioctx[i])) break; printf("io_setup(%d, ): %d calls with rc 0, last call with rc %d.\n", nr_events, i, rc); fflush(stdout); sleep(1); return 0; } """ Test-suite: libaio # curl https://kojipkgs.fedoraproject.org//packages/libaio/0.3.110/7.fc26/src/libaio-0.3.110-7.fc26.src.rpm \ | rpm2cpio | cpio -mid # tar xf libaio-0.3.110.tar.gz # cd libaio-0.3.110 # make # make check 2>&1 | grep '^test cases' test cases/2.t completed PASSED. test cases/3.t completed PASSED. test cases/4.t completed PASSED. test cases/5.t completed PASSED. test cases/6.t completed PASSED. test cases/7.t completed PASSED. test cases/11.t completed PASSED. test cases/12.t completed PASSED. test cases/13.t completed PASSED. test cases/14.t completed PASSED. test cases/15.t completed PASSED. test cases/16.t completed PASSED. test cases/10.t completed PASSED. test cases/8.t completed PASSED. Signed-off-by: Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com> Reported-by: Lekshmi C. Pillai <lekshmi.cpillai@in.ibm.com> Tested-by: Lekshmi C. Pillai <lekshmi.cpillai@in.ibm.com> Tested-by: Paul Nguyen <nguyenp@us.ibm.com> --- fs/aio.c | 19 ++++++++++++------- 1 file changed, 12 insertions(+), 7 deletions(-)