Oracle’s Lorenzo Stoakes has recently introduced a series of patches aimed at enhancing the efficiency of guard pages in the Linux kernel. Guard pages, commonly utilized by userland library functions like allocators and threading mechanisms, are meant to protect certain regions of memory by sending a fatal signal if accessed improperly. Traditionally, these are created using `PROT_NONE` `mmap()` mappings, each consuming a Virtual Memory Area (VMA), which can cumulatively lead to substantial memory overhead, particularly in systems running many processes and threads.
Stoakes’s new approach, suggested by multiple developers including Vlasimil Babka, David Hildenbrand, and Jann Horn, proposes embedding the guard pages directly within the page tables that map the required memory ranges instead of at the VMA layer. This adjustment promises to streamline the memory mapping process, evidenced by early tests showing a fivefold increase in speed when using memory mapping functions alongside `process_madvise()`. Additionally, these tests on an idle Android system with unoptimized code have revealed a 13% reduction in VMAs.
The implications of such enhancements could be substantial, particularly for systems that handle large numbers of guard pages. While the initial results are promising, further optimization could potentially amplify these benefits.
For those interested in the specifics of these lightweight guard pages and their implementation, more details are available in the full patch series at Phoronix.