On Thu, Jun 11, 2026 at 12:01:55PM +0200, David Hildenbrand (Arm) wrote: >The droppable test currently relies on creating memory pressure in a >child process to trigger dropping the droppable pages. > >That not only takes a long time on some machines (allocating and filling >all that memory), on large machines this will not work as we hardcode the >area size to 134217728 bytes. > >... further, we rely on timeouts to detect that memory was not dropped, >which is really suboptimal. > >Instead, let's just use MADV_PAGEOUT on a 2 MiB region. MADV_PAGEOUT works >with droppable memory even without swap. > >There is the low chance of MADV_PAGEOUT failing to drop a page because >of speculative references. We'll wait 1s and retry 10 times to >rule that unlikely case out as best as we can. > >On a machine without swap: > > $ ./droppable > TAP version 13 > 1..1 > ok 1 madvise(MADV_PAGEOUT) behavior > # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 > >Reported-by: Aishwarya TCV <[email protected]> >Fixes: 9651fcedf7b9 ("mm: add MAP_DROPPABLE for designating always lazily >freeable mappings") >Signed-off-by: David Hildenbrand (Arm) <[email protected]> >---
Cool! Tested with swap both off and on, and it passed either way :D That's what I'd expect, VM_DROPPABLE folios stay anon + non-swapbacked, so reclaim can discard them instead of swapping them out :) Tested-by: Lance Yang <[email protected]>
