On Wed, Jul 6, 2022 at 5:06 PM Zach O'Keefe <zokeefe@xxxxxxxxxx> wrote: > > Add PMDMappable field to smaps output which informs the user if memory > in the VMA can be PMD-mapped by MADV_COLLAPSE. > > The distinction from THPeligible is needed for two reasons: > > 1) For THP, MADV_COLLAPSE is not coupled to THP sysfs controls, which > THPeligible reports. > > 2) PMDMappable can also be used in HugeTLB fine-granularity mappings, > which are independent from THP. Could you please elaborate the usecase? The user checks this hint before calling MADV_COLLAPSE? Is it really necessary? And, TBH it sounds confusing and we don't have to maintain both THPeligible and PMDMappable. We could just relax THPeligible to make it return 1 even though THP is disabled by sysfs but MADV_COLLAPSE could collapse it if such hint is useful. > > Signed-off-by: Zach O'Keefe <zokeefe@xxxxxxxxxx> > --- > Documentation/filesystems/proc.rst | 10 ++++++++-- > fs/proc/task_mmu.c | 2 ++ > 2 files changed, 10 insertions(+), 2 deletions(-) > > diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst > index 47e95dbc820d..f207903a57a5 100644 > --- a/Documentation/filesystems/proc.rst > +++ b/Documentation/filesystems/proc.rst > @@ -466,6 +466,7 @@ Memory Area, or VMA) there is a series of lines such as the following:: > MMUPageSize: 4 kB > Locked: 0 kB > THPeligible: 0 > + PMDMappable: 0 > VmFlags: rd ex mr mw me dw > > The first of these lines shows the same information as is displayed for the > @@ -518,9 +519,14 @@ replaced by copy-on-write) part of the underlying shmem object out on swap. > does not take into account swapped out page of underlying shmem objects. > "Locked" indicates whether the mapping is locked in memory or not. > > +"PMDMappable" indicates if the memory can be mapped by PMDs - 1 if true, 0 > +otherwise. It just shows the current status. Note that this is memory > +operable on explicitly by MADV_COLLAPSE. > + > "THPeligible" indicates whether the mapping is eligible for allocating THP > -pages as well as the THP is PMD mappable or not - 1 if true, 0 otherwise. > -It just shows the current status. > +pages by the kernel, as well as the THP is PMD mappable or not - 1 if true, 0 > +otherwise. It just shows the current status. Note this is memory the kernel can > +transparently provide as THPs. > > "VmFlags" field deserves a separate description. This member represents the > kernel flags associated with the particular virtual memory area in two letter > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > index f8cd58846a28..29f2089456ba 100644 > --- a/fs/proc/task_mmu.c > +++ b/fs/proc/task_mmu.c > @@ -867,6 +867,8 @@ static int show_smap(struct seq_file *m, void *v) > > seq_printf(m, "THPeligible: %d\n", > hugepage_vma_check(vma, vma->vm_flags, true, false, true)); > + seq_printf(m, "PMDMappable: %d\n", > + hugepage_vma_check(vma, vma->vm_flags, true, false, false)); > > if (arch_pkeys_enabled()) > seq_printf(m, "ProtectionKey: %8u\n", vma_pkey(vma)); > -- > 2.37.0.rc0.161.g10f37bed90-goog >
