On Mon, Feb 10, 2025 at 04:37:36PM -0800, Andrew Morton wrote: > On Mon, 10 Feb 2025 18:09:48 +0800 I Hsin Cheng <richard120310@xxxxxxxxx> wrote: > > > When !start_pte is true, the branch for "start_pte" in "out_ptl" label > > section is surely false, and "ptl != pml" must be true since "ptl" is > > NULL in this case. > > > > It means both branches in "out_ptl" are redundant, only one thing to be > > done is to unlock "pml", make it directly unlock "pml" and return in > > this case. > > Hopefully the compiler will skip the `if (start_pte)' test. > > Generally, we try to avoid multiple function return points. We could do > > --- a/mm/pt_reclaim.c~mm-pgtable-unlock-pml-without-branches-when-start_pte > +++ a/mm/pt_reclaim.c > @@ -43,7 +43,7 @@ void try_to_free_pte(struct mm_struct *m > pml = pmd_lock(mm, pmd); > start_pte = pte_offset_map_rw_nolock(mm, pmd, addr, &pmdval, &ptl); > if (!start_pte) > - goto out_ptl; > + goto out_unlock; > if (ptl != pml) > spin_lock_nested(ptl, SINGLE_DEPTH_NESTING); > > @@ -67,5 +67,6 @@ out_ptl: > if (start_pte) > pte_unmap_unlock(start_pte, ptl); > if (ptl != pml) > +out_unlock: > spin_unlock(pml); > } > _ > > but that's really ugly. Hi Andrew, Thanks for your review! > if (ptl != pml) > +out_unlock: > spin_unlock(pml); > } > _ > > but that's really ugly. I agree. Would you be so nice to suggest some test method for me so I can try to test how much benefit we can get from this? If the case happens frequently enough I think it might be worth it? Best regards, I Hsin Cheng
