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The scan is called with mmap_lock held for reading and returns > with it still held. The collapse is called without it. > > collapse_single_pmd() kept that boundary inside itself. It dropped the > lock on some paths and not others, and reported which by way of a bool it= s > callers had to carry along and then act on. > > Open-code it in the two callers. Each scans under the lock it already > holds and, on SCAN_SUCCEED, gives the lock up before running the collapse= . > khugepaged's lock_dropped and madvise_collapse()'s mmap_unlocked both go: > the code dropping the lock is now the code that wanted to know. > > khugepaged's walk carries on to the next table while the scan keeps > refusing, and ends once a collapse has taken the lock from under it. > madvise_collapse() re-finds its VMA after a collapse, which it did before= , > and now uses a NULL vma to say that it has to. It still reports the drop > to its own caller, from the line that does it. > > The lock is given up and taken again at the same points as before. No > functional change. > > Assisted-by: LLM > Signed-off-by: Kiryl Shutsemau (Meta) > --- > mm/khugepaged.c | 102 +++++++++++++++++++++++------------------------- > 1 file changed, 49 insertions(+), 53 deletions(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index c26907300c23..9bdf12128357 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -2857,28 +2857,6 @@ static enum scan_result collapse_run_pmd(struct mm= _struct *mm, > return result; > } > =20 > -/* > - * Try to collapse a single PMD starting at a PMD aligned addr, and retu= rn > - * the results. > - */ > -static enum scan_result collapse_single_pmd(unsigned long addr, > - struct vm_area_struct *vma, bool *lock_dropped, > - struct collapse_control *cc) > -{ > - struct mm_struct *mm =3D vma->vm_mm; > - enum scan_result result; > - > - result =3D collapse_scan_pmd(vma, addr, cc); > - if (result !=3D SCAN_SUCCEED) > - return result; > - > - /* The collapse takes its own locks, so give this up */ > - mmap_read_unlock(mm); > - *lock_dropped =3D true; > - > - return collapse_run_pmd(mm, addr, cc); > -} > - Sorry for walking back on this. I think collapse_single_pmd() can be kept and still get patch 10 to 12 applied. The reason is that by looking at= the code after patch 11 is applied, the collapse_scan_pmd() + collapse_run_pmd() patterns in madvise_collapse() and collapse_scan_mm_slot() look very similar. And it can make collapse_scan_pmd() and collapse_run_pmd() internal with only collapse_single_pmd() exported. --=20 Best Regards, Yan, Zi