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Date: Wed, 29 Mar 2017 13:10:01 +0200 From: Ilya Dryomov <idryomov@...il.com> To: Michal Hocko <mhocko@...nel.org> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, stable@...r.kernel.org, Sergey Jerusalimov <wintchester@...il.com>, Jeff Layton <jlayton@...hat.com>, linux-xfs@...r.kernel.org Subject: Re: [PATCH 4.4 48/76] libceph: force GFP_NOIO for socket allocations On Wed, Mar 29, 2017 at 12:55 PM, Michal Hocko <mhocko@...nel.org> wrote: > On Wed 29-03-17 12:41:26, Michal Hocko wrote: > [...] >> > ceph_con_workfn >> > mutex_lock(&con->mutex) # ceph_connection::mutex >> > try_write >> > ceph_tcp_connect >> > sock_create_kern >> > GFP_KERNEL allocation >> > allocator recurses into XFS, more I/O is issued > > One more note. So what happens if this is a GFP_NOIO request which > cannot make any progress? Your IO thread is blocked on con->mutex > as you write below but the above thread cannot proceed as well. So I am > _really_ not sure this acutally helps. This is not the only I/O worker. A ceph cluster typically consists of at least a few OSDs and can be as large as thousands of OSDs. This is the reason we are calling sock_create_kern() on the writeback path in the first place: pre-opening thousands of sockets isn't feasible. Thanks, Ilya
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