Lines Matching +full:read +full:- +full:only

1 .\" SPDX-License-Identifier: BSD-2-Clause
34 .Nd safe memory reclamation for lock-free data structures
74 memory-safe lock-free data structures.
75 In typical usage, read accesses to an SMR-protected data structure, such as a
77 .Dq read section
85 In contrast with reader-writer locks such as
91 Readers can always enter a read section immediately
96 so mutations do not introduce read latency.
101 operate only on per-CPU data and thus avoid some of the performance problems
102 inherent in the implementation of traditional reader-writer mutexes.
104 accessed frequently but are only rarely modified.
106 Note that any SMR-protected data structure must be implemented carefully such
109 The data structure must be designed to be lock-free; SMR merely facilitates
117 This requirement results in a two-phase approach to the removal of items:
123 SMR provides this mechanism: readers may access a lock-free data structure in
128 functions, which together create a read section, and the
134 functions can be used to wait for threads in read sections to finish.
137 state block which holds both per-CPU and global state.
138 Readers load global state and modify per-CPU state, while writers must scan all
139 per-CPU states to detect active readers.
141 performance in write-heavy workloads.
143 Threads enter a read section by calling
145 Read sections should be short, and many operations are not permitted while in
146 a read section.
151 the duration of the read section.
152 Furthermore, read sections may not be nested: it is incorrect to call
156 state block when already in a read section for that state block.
160 kernel memory allocator provides some SMR-specified facilities.
171 To insert an item into an SMR-protected data structure, memory is allocated
179 Read-only lookup operations are performed in SMR read sections.
182 their read sections before recycling that item's memory.
184 If the zone has an associated per-item destructor, it will be invoked at some
191 Consumers are expected to use SMR in conjunction with UMA and thus need only
198 However, an introduction to the write-side interface of SMR can be useful.
203 When entering a read section,
205 loads a copy of the write sequence and stores it in per-CPU memory, hence
208 To exit a read section, this per-CPU memory is overwritten with an invalid
231 is a non-blocking operation and returns true only if all active readers are
243 This is an expensive operation and should only be used if polling cannot be
269 memory-safe read-only access to a data structure concurrent with modifications