On 29 Apr 2026, at 11:35, Zi Yan wrote: > collapse_file() is capable of collapsing pagecache folios from writable > files to PMD folios. Now enable clean pagecache folio collapse in addition > to read-only pagecache folio collapse by removing the > inode_is_open_for_write() from file_thp_enabled() and only performing > filemap_flush() if the file is read-only. > > This means userspace needs to explicitly flush the content of pagecache > folios before khugepaged can collapse the folios, or use > madvise(MADV_COLLAPSE), which does the flush in the retry. The reason is > that blindly enabling dirty pagecache folio from writable files collapse > makes khugepaged flush these folios all the time. It is undesirable to > cause system level pagecache flushes. > > To properly support dirty pagecache folio collapse, filemap_flush() needs > to be avoided. Potentially, merging associated buffer instead of dropping > it with filemap_release_folio() might be needed. > > NOTE: this breaks khugepaged selftests for writable file pagecache > collapse, which is set to fail all the time. The next commit fix it.
Sashiko: Is it acceptable to intentionally break the selftests in this commit? Each commit should be self-contained and not knowingly introduce test regressions, as this breaks bisectability. Answer: I am fine with squashing patch 14 into this one, but it is unlikely anyone gets a kernel at exact this commit. Best Regards, Yan, Zi
