dm bufio: check new buffer allocation watermark every 30 seconds
authorMikulas Patocka <mpatocka@redhat.com>
Sun, 30 Apr 2017 21:34:53 +0000 (17:34 -0400)
committerMike Snitzer <snitzer@redhat.com>
Mon, 1 May 2017 19:21:42 +0000 (15:21 -0400)
commit390020ad2af9ca04844c4f3b1f299ad8746d84c8
treea89be3c8cd0ad3b0959c12eb534c288be9669597
parent1b0fb5a5b2dc0dddcfa575060441a7176ba7ac37
dm bufio: check new buffer allocation watermark every 30 seconds

dm-bufio checks a watermark when it allocates a new buffer in
__bufio_new().  However, it doesn't check the watermark when the user
changes /sys/module/dm_bufio/parameters/max_cache_size_bytes.

This may result in a problem - if the watermark is high enough so that
all possible buffers are allocated and if the user lowers the value of
"max_cache_size_bytes", the watermark will never be checked against the
new value because no new buffer would be allocated.

To fix this, change __evict_old_buffers() so that it checks the
watermark.  __evict_old_buffers() is called every 30 seconds, so if the
user reduces "max_cache_size_bytes", dm-bufio will react to this change
within 30 seconds and decrease memory consumption.

Depends-on: 1b0fb5a5b2 ("dm bufio: avoid a possible ABBA deadlock")
Cc: stable@vger.kernel.org
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
drivers/md/dm-bufio.c