git: kernel - Reduce vm_page_list_find2() stalls
dillon at crater.dragonflybsd.org
Tue Feb 26 08:49:56 PST 2019
Author: Matthew Dillon <dillon at apollo.backplane.com>
Date: Mon Feb 25 22:58:24 2019 -0800
kernel - Reduce vm_page_list_find2() stalls
* Reduce stalls in vm_page_list_find2() which can occur in low-memory
situations, as well as in other situations. The problem is two fold.
First, that potentially all cpu cores can wind up waiting for a
single vm_page's spin-lock to be released.
Second, that a long-held vm_page spin-lock can cause the VM system
to stall unnecessarily long.
* Change vm_page_list_find() and vm_page_list_find2() to no longer
unconditionally spinlock a vm_page candidate and then retry if it
is found to be on the wrong queue.
Instead the code now spinlocks the queue, then iterates vm_page
candidates using spin_trylock(), skipping any pages whos spinlocks
cannot be immediately acquired. This is lock-order-reversed but
is ok because we use trylock. Also, by locking the queue first we
guarantee that a successfully spinlocked vm_page will be on the
* Should also reduce IPIQ drain stalls reported to the console as
shown below. The %rip sample is often found in vm_page_list_find2().
send_ipiq X->Y tgt not draining (STALL_SECONDS)
Summary of changes:
sys/vm/vm_page.c | 60 ++++++++++++++++++++++++++++++++++++--------------------
1 file changed, 39 insertions(+), 21 deletions(-)
DragonFly BSD source repository
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