Messages in this thread | | | From | "Uladzislau Rezki (Sony)" <> | Subject | [PATCH 00/24] Introduce kvfree_rcu(1 or 2 arguments) | Date | Tue, 28 Apr 2020 22:58:39 +0200 |
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Motivation ---------- There were some discussions and demand in having kvfree_rcu() interface for different purposes. Basically to have a simple interface like:
<snip> void *ptr = kvmalloc(some_bytes, GFP_KERNEL); if (ptr) kvfree_rcu(ptr); <snip>
For example, please have a look at ext4 discussion here: https://lkml.org/lkml/2020/2/19/1372
due to lack of the interface that is in question, the ext4 specific workaround has been introduced, to kvfree() after a grace period:
<snip> void ext4_kvfree_array_rcu(void *to_free) { struct ext4_rcu_ptr *ptr = kzalloc(sizeof(*ptr), GFP_KERNEL);
if (ptr) { ptr->ptr = to_free; call_rcu(&ptr->rcu, ext4_rcu_ptr_callback); return; } synchronize_rcu(); kvfree(ptr); } <snip>
there are also similar places there which could be replaced by the new interface, that is much more efficient then just call synchronize_rcu() and release a memory.
Please have a look at another places in the kernel where people do not embed the rcu_head into their stuctures for some reason and do like:
<snip> synchronize_rcu(); kfree(p); <snip>
<snip> urezki@pc638:~/data/coding/linux-rcu.git$ find ./ -name "*.c" | xargs grep -C 1 -rn "synchronize_rcu" | grep kfree ./fs/nfs/sysfs.c-113- kfree(old); ./fs/ext4/super.c-1708- kfree(old_qname); ./kernel/trace/ftrace.c-5079- kfree(direct); ./kernel/trace/ftrace.c-5156- kfree(direct); ./kernel/trace/trace_probe.c-1087- kfree(link); ./kernel/module.c-3910- kfree(mod->args); ./net/core/sysctl_net_core.c-143- kfree(cur); ./arch/x86/mm/mmio-mod.c-314- kfree(found_trace); ./drivers/mfd/dln2.c-183- kfree(i); ./drivers/block/drbd/drbd_state.c-2074- kfree(old_conf); ./drivers/block/drbd/drbd_nl.c-1689- kfree(old_disk_conf); ./drivers/block/drbd/drbd_nl.c-2522- kfree(old_net_conf); ./drivers/block/drbd/drbd_nl.c-2935- kfree(old_disk_conf); ./drivers/block/drbd/drbd_receiver.c-3805- kfree(old_net_conf); ./drivers/block/drbd/drbd_receiver.c-4177- kfree(old_disk_conf); ./drivers/ipack/carriers/tpci200.c-189- kfree(slot_irq); ./drivers/crypto/nx/nx-842-pseries.c-1010- kfree(old_devdata); ./drivers/net/ethernet/myricom/myri10ge/myri10ge.c-3583- kfree(mgp->ss); ./drivers/net/ethernet/mellanox/mlx5/core/fpga/tls.c:286: synchronize_rcu(); /* before kfree(flow) */ ./drivers/net/ethernet/mellanox/mlxsw/core.c-1574- kfree(rxl_item); ./drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c-6642- kfree(adapter->mbox_log); ./drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c-6644- kfree(adapter); ./drivers/infiniband/hw/hfi1/sdma.c-1337- kfree(dd->per_sdma); ./drivers/infiniband/core/device.c:2164: * synchronize_rcu before the netdev is kfreed, so we ./drivers/misc/vmw_vmci/vmci_context.c-692- kfree(notifier); ./drivers/misc/vmw_vmci/vmci_event.c-213- kfree(s); ./drivers/staging/fwserial/fwserial.c-2122- kfree(peer); urezki@pc638:~/data/coding/linux-rcu.git$ <snip>
so all of it can be replaced by the introduced interface and that is actually aim and motivation. All that can replaced by the single kvfree_rcu() logic.
As for double argument of the kvfree_rcu() we have only one user so far, it is "mm/list_lru.c". But it costs nothing to add it.
Description ----------- This small series introduces kvfree_rcu() macro that is used for free memory after a grace period. It can be called either with one or two arguments. kvfree_rcu() as it derives from its name can handle two types of pointers, SLAB and vmalloc ones.
As a result we get two ways how to use kvfree_rcu() macro, see below two examples.
a) kvfree_rcu(ptr, rhf); struct X { struct rcu_head rhf; unsigned char data[100]; };
void *ptr = kvmalloc(sizeof(struct X), GFP_KERNEL); if (ptr) kvfree_rcu(ptr, rhf);
b) kvfree_rcu(ptr); void *ptr = kvmalloc(some_bytes, GFP_KERNEL); if (ptr) kvfree_rcu(ptr);
Last one, we name it headless variant, only needs one argument, means it does not require any rcu_head to be present within the type of ptr. There is a restriction the (b) context has to fall into might_sleep() annotation. To check that, please activate the CONFIG_DEBUG_ATOMIC_SLEEP option in your kernel.
This series is based on: git://git.kernel.org/pub/scm/linux/kernel/git/jfern/linux.git "origin/rcu/dev" branch, what is the same as Paul's almost latest dev.2020.04.13c branch.
Appreciate for any comments and feedback.
Joel Fernandes (Google) (5): rcu/tree: Keep kfree_rcu() awake during lock contention rcu/tree: Skip entry into the page allocator for PREEMPT_RT rcu/tree: Use consistent style for comments rcu/tree: Simplify debug_objects handling rcu/tree: Make kvfree_rcu() tolerate any alignment
Sebastian Andrzej Siewior (1): rcu/tree: Use static initializer for krc.lock
Uladzislau Rezki (Sony) (18): rcu/tree: Repeat the monitor if any free channel is busy rcu/tree: Simplify KFREE_BULK_MAX_ENTR macro rcu/tree: move locking/unlocking to separate functions rcu/tree: cache specified number of objects rcu/tree: add rcutree.rcu_min_cached_objs description rcu/tree: Maintain separate array for vmalloc ptrs rcu/tiny: support vmalloc in tiny-RCU rcu: Rename rcu_invoke_kfree_callback/rcu_kfree_callback rcu: Rename __is_kfree_rcu_offset() macro rcu: Rename kfree_call_rcu() to the kvfree_call_rcu(). mm/list_lru.c: Rename kvfree_rcu() to local variant rcu: Introduce 2 arg kvfree_rcu() interface mm/list_lru.c: Remove kvfree_rcu_local() function rcu/tree: Support reclaim for head-less object rcu/tiny: move kvfree_call_rcu() out of header rcu/tiny: support reclaim for head-less object rcu: Introduce 1 arg kvfree_rcu() interface lib/test_vmalloc.c: Add test cases for kvfree_rcu()
.../admin-guide/kernel-parameters.txt | 8 + include/linux/rcupdate.h | 53 +- include/linux/rcutiny.h | 6 +- include/linux/rcutree.h | 2 +- include/trace/events/rcu.h | 8 +- kernel/rcu/tiny.c | 168 ++++++- kernel/rcu/tree.c | 454 +++++++++++++----- lib/test_vmalloc.c | 103 +++- mm/list_lru.c | 11 +- 9 files changed, 662 insertions(+), 151 deletions(-)
-- 2.20.1
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