On Fri, Aug 18, 2023 at 03:14:02PM -0700, Zach O'Keefe wrote: > Sorry -- noticed only too late that there are still many > false-negatives for THPeligible, since by this point in the function > we've already applied sysfs and prctl restrictions, which file-fault > ignores. VM_HUGEPAGE also needs to be checked for the file-fault case. I'm not entirely convinced that unifying all of these things leads to code that's simpler to understand. > On Fri, Aug 18, 2023 at 2:15 PM Zach O'Keefe <zokeefe@xxxxxxxxxx> wrote: > > > > File-backed memory can be backed by THPs either through collapse, when > > CONFIG_READ_ONLY_THP_FOR_FS is enabled, or through fault, when the > > filesystem supports large folio mappings. > > > > Currently, smaps only knows about the former, so teach it about the > > latter. > > > > Signed-off-by: Zach O'Keefe <zokeefe@xxxxxxxxxx> > > Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> > > --- > > mm/huge_memory.c | 11 ++++++++++- > > 1 file changed, 10 insertions(+), 1 deletion(-) > > > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > > index cd379b2c077b..d8d6e83820f3 100644 > > --- a/mm/huge_memory.c > > +++ b/mm/huge_memory.c > > @@ -136,7 +136,16 @@ bool hugepage_vma_check(struct vm_area_struct *vma, unsigned long vm_flags, > > */ > > !!vma->vm_ops->huge_fault : > > /* Only regular file is valid in collapse path */ > > - file_thp_enabled(vma); > > + file_thp_enabled(vma) || > > + /* > > + * THPeligible bit of smaps should surface the > > + * possibility of THP through fault if the filesystem > > + * supports it. We don't check this in fault path, > > + * because we want to fallback to the actual ->fault() > > + * handler to make the decision. > > + */ > > + (smaps && vma->vm_file && > > + mapping_large_folio_support(vma->vm_file->f_mapping)); > > > > if (vma_is_temporary_stack(vma)) > > return false; > > -- > > 2.42.0.rc1.204.g551eb34607-goog > >
