Hi, On 2026-04-10 11:18:24 -0400, Zi Yan wrote: > On 10 Apr 2026, at 11:06, Andres Freund wrote: > > On 2026-03-26 21:42:50 -0400, Zi Yan wrote: > >> Replace it with a check on the max folio order of the file's address space > >> mapping, making sure PMD_ORDER is supported. > > > > Question from a user space developer (who learned of this via LWN [1]): > > > > Right now MADV_COlLAPSE on file mappings appears to only only work with > > CONFIG_READ_ONLY_THP_FOR_FS. > > > > That's pretty sad, because I see quite consistent gains (~15%) from doing > > madvise(MADV_COLLAPSE) on e.g. postgres' .text - but because > > CONFIG_READ_ONLY_THP_FOR_FS is not enabled default (or at least not > > commonly, > > I think?) in distro kernels, it never quite seemed worth the fiddliness. > > > > > > Do I understand correctly that by replacing the check here (and the > > predecessor commits), madvise(MADV_COLLAPSE) on file mappings might actually > > start working in more situations on typical distro kernels? > > Yes, assuming your file system supports PMD THPs. > > Based on[1], ext4 and xfs have the support, btrfs supports large folio but > not up to PMD order. I have not checked other FSes supporting large folio[2].
I personally only care about ext4 and xfs, so this is awesome. Thanks, Andres
