Hello all, Please help me to clarify what will page fault handler do (if any) File arch/x86/include/asm/pgtable_types.h have following comment for 2 PAGE_DIRTY_BITs #define _PAGE_BIT_DIRTY 6 /* was written to (raised by CPU) */ _PAGE_BIT_SOFT_DIRTY _PAGE_BIT_SOFTW3 /* software dirty tracking */ While documentation clearly explains that Page Fault handler sets second flag https://www.kernel.org/doc/Documentation/vm/soft-dirty.txt I do not have idea what will happen when tracking Soft Dirty flags is off, I suppose the answer is in mm/gup.c but I was not able to track it to page handler. Thanks you all. Lev.