[LU-12179] allocate continuous pages when disabled page caches

• Type: Improvement
• Resolution: Unresolved
• Priority: Minor
• Assignee: Qian Yingjin
• Reporter: Qian Yingjin

Description

LU-11347: Do not use pagecache for SSD I/O when read/write cache are disabled, 

this feature allocates the physical pages per OSS I/O thread in need at the runtime, it may result that  the many allocated pages are  not physical continuous. This may be not good for I/O merge in the block layer due to the limited segements per block I/O request.

For testing purposes, we should pre-allocate continuous pages when OSS thread started as much as possible when disable page chace.

Issue Links

• is related to: LU-11347 Do not use pagecache for SSD I/O when read/write cache are disabled
• is related to: LU-12071 bypass pagecache for large files
• is related to: LU-13309 performance optimizations for brw