Subject: Re: [PATCH rdma-next v3 00/11] RDMA/core: Introduce FRMR pools infrastructure

From: Leon Romanovsky <[email-masked]>
Date: Wed, 25 Feb 2026 13:47:16 +0200

On Mon, Feb 02, 2026 at 05:59:52PM +0200, Edward Srouji wrote:
> From Michael:
> 
> This patch series introduces a new FRMR (Fast Registration Memory Region)
> pool infrastructure for the RDMA core subsystem. The goal is to provide
> efficient management and allow reuse of MRs (Memory Regions) for RDMA
> device drivers.
> 
> Background
> ==========
> 
> Memory registration and deregistration can be a significant bottleneck in
> RDMA applications that need to register memory regions dynamically in
> their data path or must re-register memory on application restart.
> Repeatedly allocating and freeing these resources introduces overhead,
> particularly in high-throughput or latency-sensitive environments where
> memory regions are frequently cycled. Notably, the mlx5_ib driver has
> already adopted memory registration reuse mechanisms and has demonstrated
> notable performance improvements as a result.
> 
> FRMR pools will store handles of the reusable objects, giving drivers
> the flexibility to choose what to store (e.g: pointers or indexes).
> Device driver integration requires the ability to modify the hardware
> objects underlying MRs when reusing FRMR handles, allowing the update
> of pre-allocated handles to fit the parameters of requested MR
> registrations. The FRMR pools manage memory region handles with respect
> to attributes that cannot be changed after allocation such as access flags,
> ATS capabilities, vendor keys, and DMA block size so each pool is uniquely
> characterized by these non-modifiable attributes.
> This ensures compatibility and correctness while allowing drivers
> flexibility in managing other aspects of the MR lifecycle.
> 
> Solution Overview
> =================
> 
> This patch series introduces a centralized, per-device FRMR pooling
> infrastructure that provides:
> 
> 1. Pool Organization: Uses an RB-tree to organize pools by FRMR
>    characteristics (ATS support, access flags, vendor-specific keys,
>    and DMA block count). This allows efficient lookup and reuse of
>    compatible FRMR handles.
> 
> 2. Dynamic Allocation: Pools grow dynamically on demand when no cached
>    handles are available, ensuring optimal memory usage without
>    sacrificing performance.
> 
> 3. Aging Mechanism: Implements an aging system. Unused handles are
>    gradually moved to the freed after a configurable aging period
>    (default: 60 seconds), preventing memory bloat during idle periods.
> 
> 4. Pinned Handles: Supports pinning a minimum number of handles per
>    pool to maintain performance for latency-sensitive workloads, avoiding
>    allocation overhead on critical paths.
> 
> 5. Driver Flexibility: Provides a callback-based interface
>    (ib_frmr_pool_ops) that allows drivers to implement their own FRMR
>    creation/destruction logic while leveraging the common pooling
>    infrastructure.
> 
> API
> ===
> 
> The infrastructure exposes the following APIs:
> 
> - ib_frmr_pools_init(): Initialize FRMR pools for a device
> - ib_frmr_pools_cleanup(): Clean up all pools for a device
> - ib_frmr_pool_pop(): Get an FRMR handle from the pool
> - ib_frmr_pool_push(): Return an FRMR handle to the pool
> - ib_frmr_pools_set_aging_period(): Configure aging period
> - ib_frmr_pools_set_pinned(): Set minimum pinned handles per pool
> 
> mlx5_ib
> =======
> 
> The partial control and visability we had only over the 'persistent'
> cache entries through debugfs is replaced by the netlink FRMR API that
> allows showing and setting properties of all available pools.
> This series also changes the default behavior MR cache had for PFs
> (Physical Functions) by dropping the pre-allocation of MKEYs that was
> costing 100MB of memory per PF and slowing down the loading and
> unloading of the driver.
> 
> Signed-off-by: Michael Guralnik <[email-masked]>
> Signed-off-by: Edward Srouji <[email-masked]>
> ---
> Changes in v3:
> - Use rbtree helpers for pool find and find_add operations.
> - Use cmp_int() for pool key comparison.
> - Make key comparison inline.
> - Link to v2: https://lore.kernel.org/r/[email-masked]
> 
> Changes in v2:
> - Fix stack size warning in netlink set_pinned flow.
> - Add commit to move async command context init and cleanup out of MR
>   cache logic.
> - Add enforcement of access flags in set_pinned flow and enforce used
>   bits in vendor specific fields to ensure old kernels fail if any
>   unknown parameter is passed.
> - Add an option to expose kernel-internal pools through netlink.
> - Link to v1: https://lore.kernel.org/r/[email-masked]
> 
> ---
> Chiara Meiohas (1):
>       RDMA/mlx5: Move device async_ctx initialization
> 
> Michael Guralnik (10):
>       IB/core: Introduce FRMR pools
>       RDMA/core: Add aging to FRMR pools
>       RDMA/core: Add FRMR pools statistics
>       RDMA/core: Add pinned handles to FRMR pools
>       RDMA/mlx5: Switch from MR cache to FRMR pools
>       net/mlx5: Drop MR cache related code
>       RDMA/nldev: Add command to get FRMR pools
>       RDMA/core: Add netlink command to modify FRMR aging
>       RDMA/nldev: Add command to set pinned FRMR handles
>       RDMA/nldev: Expose kernel-internal FRMR pools in netlink

There is a need to rebase this series, it doesn't apply.

Thanks