I'm sorry for the delay in replying your mail. <91411837-8c65-bf7d-7ca3-d69bdcb49...@iki.fi> Thu, 1 Mar 2018 18:40:05 +0800Heikki Linnakangas <hlinn...@iki.fi> wrote : >Interesting. How does this compare with using good old mmap()?
The libpmem's pmem_map_file() supported 2M/1G(the size of huge page) alignment, since it could reduce the number of page faults. In addition, libpmem's pmem_memcpy_nodrain() is the function to copy data using single instruction, multiple data(SIMD) instructions and NT store instructions(MOVNT). As a result, using these APIs is faster than using old mmap()/memcpy(). Please see the PGCon2018 presentation[1] for the details. [1] https://www.pgcon.org/2018/schedule/attachments/507_PGCon2018_Introducing_PMDK_into_PostgreSQL.pdf <83eafbfd-d9c5-6623-2423-7cab1be38...@iki.fi> Fri, 20 Jul 2018 23:18:05 +0300Heikki Linnakangas <hlinn...@iki.fi> wrote : >I think the way forward with this patch would be to map WAL segments >with plain old mmap(), and use msync(). If that's faster than the status >quo, great. If not, it would still be a good stepping stone for actually >using PMDK. I think so too. I wrote this patch to replace read/write syscalls with libpmem's API only. I believe that PMDK can make the current PostgreSQL faster. > If nothing else, it would provide a way to test most of the >code paths, without actually having a persistent memory device, or >libpmem. The examples at http://pmem.io/pmdk/libpmem/ actually sugest >doing exactly that: use libpmem to map a file to memory, and check if it >lives on persistent memory using libpmem's pmem_is_pmem() function. If >it returns yes, use pmem_drain(), if it return false, fall back to using >msync(). When PMEM_IS_PMEM_FORCE(the environment variable[2]) is set to 1, pmem_is_pmem() return yes. Linux 4.15 and more supported MAP_SYNC and MAP_SHARED_VALIDATE of mmap() flags to check if the mapped file is stored on PMEM. An application that used both flags in its mmap() call can be sure that MAP_SYNC is actually supported by both the kernel and the filesystem that the mapped file is stored in[3]. But pmem_is_pmem() doesn't support this mechanism for now. [2] http://pmem.io/pmdk/manpages/linux/v1.4/libpmem/libpmem.7.html [3] https://lwn.net/Articles/758594/ -- Yoshimi Ichiyanagi NTT Software Innovation Center e-mail : ichiyanagi.yosh...@lab.ntt.co.jp
