| Message ID | 20240515125342.1069999-4-haakon.bugge@oracle.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | rds: rdma: Add ability to force GFP_NOIO | expand |
On 15.05.24 14:53, Håkon Bugge wrote: > In cma_init(), we call memalloc_noio_{save,restore} in a parenthetic > fashion when enabled by the module parameter force_noio. > > This in order to conditionally enable rdma_cm to work aligned with > block I/O devices. Any work queued later on work-queues created during > module initialization will inherit the PF_MEMALLOC_{NOIO,NOFS} > flag(s), due to commit ("workqueue: Inherit NOIO and NOFS alloc > flags"). > > We do this in order to enable ULPs using the RDMA stack to be used as > a network block I/O device. This to support a filesystem on top of a > raw block device which uses said ULP(s) and the RDMA stack as the > network transport layer. > > Under intense memory pressure, we get memory reclaims. Assume the > filesystem reclaims memory, goes to the raw block device, which calls > into the ULP in question, which calls the RDMA stack. Now, if > regular GFP_KERNEL allocations in the ULP or the RDMA stack require > reclaims to be fulfilled, we end up in a circular dependency. > > We break this circular dependency by: > > 1. Force all allocations in the ULP and the relevant RDMA stack to use > GFP_NOIO, by means of a parenthetic use of > memalloc_noio_{save,restore} on all relevant entry points. > > 2. Make sure work-queues inherits current->flags > wrt. PF_MEMALLOC_{NOIO,NOFS}, such that work executed on the > work-queue inherits the same flag(s). > > Signed-off-by: Håkon Bugge <haakon.bugge@oracle.com> > --- > drivers/infiniband/core/cma.c | 20 +++++++++++++++++--- > 1 file changed, 17 insertions(+), 3 deletions(-) > > diff --git a/drivers/infiniband/core/cma.c b/drivers/infiniband/core/cma.c > index 1e2cd7c8716e8..23a50cc3e81cb 100644 > --- a/drivers/infiniband/core/cma.c > +++ b/drivers/infiniband/core/cma.c > @@ -50,6 +50,10 @@ MODULE_LICENSE("Dual BSD/GPL"); > #define CMA_IBOE_PACKET_LIFETIME 16 > #define CMA_PREFERRED_ROCE_GID_TYPE IB_GID_TYPE_ROCE_UDP_ENCAP > > +static bool cma_force_noio; > +module_param_named(force_noio, cma_force_noio, bool, 0444); > +MODULE_PARM_DESC(force_noio, "Force the use of GFP_NOIO (Y/N)"); > + > static const char * const cma_events[] = { > [RDMA_CM_EVENT_ADDR_RESOLVED] = "address resolved", > [RDMA_CM_EVENT_ADDR_ERROR] = "address error", > @@ -5424,6 +5428,10 @@ static struct pernet_operations cma_pernet_operations = { > static int __init cma_init(void) > { > int ret; > + unsigned int noio_flags; https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/maintainer-netdev.rst?h=v6.9#n376 " Netdev has a convention for ordering local variables in functions. Order the variable declaration lines longest to shortest, e.g.:: struct scatterlist *sg; struct sk_buff *skb; int err, i; If there are dependencies between the variables preventing the ordering move the initialization out of line. " Zhu Yanjun > + > + if (cma_force_noio) > + noio_flags = memalloc_noio_save(); > > /* > * There is a rare lock ordering dependency in cma_netdev_callback() > @@ -5439,8 +5447,10 @@ static int __init cma_init(void) > } > > cma_wq = alloc_ordered_workqueue("rdma_cm", WQ_MEM_RECLAIM); > - if (!cma_wq) > - return -ENOMEM; > + if (!cma_wq) { > + ret = -ENOMEM; > + goto out; > + } > > ret = register_pernet_subsys(&cma_pernet_operations); > if (ret) > @@ -5458,7 +5468,8 @@ static int __init cma_init(void) > if (ret) > goto err_ib; > > - return 0; > + ret = 0; > + goto out; > > err_ib: > ib_unregister_client(&cma_client); > @@ -5469,6 +5480,9 @@ static int __init cma_init(void) > unregister_pernet_subsys(&cma_pernet_operations); > err_wq: > destroy_workqueue(cma_wq); > +out: > + if (cma_force_noio) > + memalloc_noio_restore(noio_flags); > return ret; > } >
Hi Yanjun, > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/maintainer-netdev.rst?h=v6.9#n376 > > " > Netdev has a convention for ordering local variables in functions. > Order the variable declaration lines longest to shortest, e.g.:: "Infiniband subsystem" != netdev, right? Thxs, Håkon
On Thu, May 16, 2024 at 11:54 PM Haakon Bugge <haakon.bugge@oracle.com> wrote: > > Hi Yanjun, > > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/maintainer-netdev.rst?h=v6.9#n376 > > > > " > > Netdev has a convention for ordering local variables in functions. > > Order the variable declaration lines longest to shortest, e.g.:: > > "Infiniband subsystem" != netdev, right? All kernel subsystems should follow this rule, including the network and rdma subsystems > > > Thxs, Håkon >
> On 16 May 2024, at 21:07, Greg Sword <gregsword0@gmail.com> wrote: > > On Thu, May 16, 2024 at 11:54 PM Haakon Bugge <haakon.bugge@oracle.com> wrote: >> >> Hi Yanjun, >> >> >>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/maintainer-netdev.rst?h=v6.9#n376 >>> >>> " >>> Netdev has a convention for ordering local variables in functions. >>> Order the variable declaration lines longest to shortest, e.g.:: >> >> "Infiniband subsystem" != netdev, right? > > All kernel subsystems should follow this rule, including the network > and rdma subsystems I am note aware. Where is this documented? Thxs, Håkon
On Fri, May 17, 2024 at 03:07:34AM +0800, Greg Sword wrote: > On Thu, May 16, 2024 at 11:54 PM Haakon Bugge <haakon.bugge@oracle.com> wrote: > > > > Hi Yanjun, > > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/maintainer-netdev.rst?h=v6.9#n376 > > > > > > " > > > Netdev has a convention for ordering local variables in functions. > > > Order the variable declaration lines longest to shortest, e.g.:: > > > > "Infiniband subsystem" != netdev, right? > > All kernel subsystems should follow this rule, including the network > and rdma subsystems Of course not. The request to sort variables is netdev coding style, rest of the kernel doesn't have this rule and doesn't care about it. In Infiniband, we accept both styles, just to make sure that people who submit their patches to both subsystems won't need to bother themselves with this. Thanks > > > > > > > Thxs, Håkon > >
diff --git a/drivers/infiniband/core/cma.c b/drivers/infiniband/core/cma.c index 1e2cd7c8716e8..23a50cc3e81cb 100644 --- a/drivers/infiniband/core/cma.c +++ b/drivers/infiniband/core/cma.c @@ -50,6 +50,10 @@ MODULE_LICENSE("Dual BSD/GPL"); #define CMA_IBOE_PACKET_LIFETIME 16 #define CMA_PREFERRED_ROCE_GID_TYPE IB_GID_TYPE_ROCE_UDP_ENCAP +static bool cma_force_noio; +module_param_named(force_noio, cma_force_noio, bool, 0444); +MODULE_PARM_DESC(force_noio, "Force the use of GFP_NOIO (Y/N)"); + static const char * const cma_events[] = { [RDMA_CM_EVENT_ADDR_RESOLVED] = "address resolved", [RDMA_CM_EVENT_ADDR_ERROR] = "address error", @@ -5424,6 +5428,10 @@ static struct pernet_operations cma_pernet_operations = { static int __init cma_init(void) { int ret; + unsigned int noio_flags; + + if (cma_force_noio) + noio_flags = memalloc_noio_save(); /* * There is a rare lock ordering dependency in cma_netdev_callback() @@ -5439,8 +5447,10 @@ static int __init cma_init(void) } cma_wq = alloc_ordered_workqueue("rdma_cm", WQ_MEM_RECLAIM); - if (!cma_wq) - return -ENOMEM; + if (!cma_wq) { + ret = -ENOMEM; + goto out; + } ret = register_pernet_subsys(&cma_pernet_operations); if (ret) @@ -5458,7 +5468,8 @@ static int __init cma_init(void) if (ret) goto err_ib; - return 0; + ret = 0; + goto out; err_ib: ib_unregister_client(&cma_client); @@ -5469,6 +5480,9 @@ static int __init cma_init(void) unregister_pernet_subsys(&cma_pernet_operations); err_wq: destroy_workqueue(cma_wq); +out: + if (cma_force_noio) + memalloc_noio_restore(noio_flags); return ret; }
In cma_init(), we call memalloc_noio_{save,restore} in a parenthetic fashion when enabled by the module parameter force_noio. This in order to conditionally enable rdma_cm to work aligned with block I/O devices. Any work queued later on work-queues created during module initialization will inherit the PF_MEMALLOC_{NOIO,NOFS} flag(s), due to commit ("workqueue: Inherit NOIO and NOFS alloc flags"). We do this in order to enable ULPs using the RDMA stack to be used as a network block I/O device. This to support a filesystem on top of a raw block device which uses said ULP(s) and the RDMA stack as the network transport layer. Under intense memory pressure, we get memory reclaims. Assume the filesystem reclaims memory, goes to the raw block device, which calls into the ULP in question, which calls the RDMA stack. Now, if regular GFP_KERNEL allocations in the ULP or the RDMA stack require reclaims to be fulfilled, we end up in a circular dependency. We break this circular dependency by: 1. Force all allocations in the ULP and the relevant RDMA stack to use GFP_NOIO, by means of a parenthetic use of memalloc_noio_{save,restore} on all relevant entry points. 2. Make sure work-queues inherits current->flags wrt. PF_MEMALLOC_{NOIO,NOFS}, such that work executed on the work-queue inherits the same flag(s). Signed-off-by: Håkon Bugge <haakon.bugge@oracle.com> --- drivers/infiniband/core/cma.c | 20 +++++++++++++++++--- 1 file changed, 17 insertions(+), 3 deletions(-)