[LU-17463] enable/disable page cache shrinker for mlocked pages on OSC layer

• Type: Bug
• Resolution: Unresolved
• Priority: Minor
• Severity: 3
• Assignee: Qian Yingjin
• Reporter: Qian Yingjin

Description

Those pages mapped into VM_LOCKED [mlock()ed] VMAs should be unevictable pages:
i.e. mlocked pages via mlock() or mlockall() (see the URL for details: https://www.kernel.org/doc/html/v4.19/vm/unevictable-lru.html).

However, OSC page cache shrinker treats all cached page equally even some of them are unelectable. It may evict the mlocked pages wrongly.

We should disable page cache shrinker to avoid it evicting mlocked pages.

Issue Links

• is related to: LU-18397 mmap reads may not correctly update LDLM extent lock usage
• is related to: LU-18226 sanity: test_600b Error: 'unevict_mb is 99, expected 100'