On 28 Apr 2026, at 16:19, David Hildenbrand (Arm) wrote: > On 4/28/26 22:17, Zi Yan wrote: >> On 28 Apr 2026, at 16:07, David Hildenbrand (Arm) wrote: >> >>> On 4/28/26 21:56, Zi Yan wrote: >>>> >>>> >>>> This patch breaks the khugepaged test for READ_ONLY_THP_FOR_FS. >>>> >>>> When I ran sudo ./khugepaged all:file ~/ on ext4, >>>> >>>> collapse_max_ptes_none (khugepaged:file) fails. >>> >>> madvise() still works? Is it maybe because of dirty folios? (but that should >>> also be the case on write ...) >> >> I asked codex instead. >> >> Basically, mmap(MMAP_SHARED) makes the written folio dirty and the folio >> survives the later drop_caches. Adding msync() fixes the issue. > > But why doesn't the write() make the folios dirty? Or are we running into some > race condition where the old code just worked by chance? >
The fd is opened with O_DSYNC, so the data from write() is transferred to disk when write() returns. Best Regards, Yan, Zi
