On Mon, Mar 23, 2026 at 04:24:26PM -0400, Zi Yan wrote:
> On 23 Mar 2026, at 16:13, David Hildenbrand (Arm) wrote:
> > I assume so, because for executables you would have to be lucky to get a
> > PMD THP? So I don't see the non-khugepaged large folio support on par
> > with khugepaged support.
Not necessarily that lucky; if you set VM_HUGEPAGE,
do_sync_mmap_readahead() will allocate PMD-sized folios automatically.
On busy database servers (and is there any other kind?), khugepaged
takes too long to run and find opportunities to collapse text pages.
Like, days.
> It is more like turning on READ_ONLY_THP_FOR_FS by default for
> FS with large folio support instead of removing it.
>
> OK, I will give it another try.
I think the test needs to be:
if (mapping_max_folio_order(mapping) >= PMD_ORDER)
as there can be cases of filesystems which support up to, say, 64KiB,
but not all the way up to 2MiB. I disapprove of this situation, but
this is where we are right now.
