Re: [PATCH mm-new v8 4/4] mm: khugepaged: skip lazy-free folios

[Vernon Yang]

On Tue, Feb 24, 2026 at 04:10:47AM +0800, Barry Song wrote:
> On Sat, Feb 21, 2026 at 9:39 PM Vernon Yang <vernon2gm@xxxxxxxxx> wrote:
> >
> > On Sat, Feb 21, 2026 at 06:27:36PM +0800, Barry Song wrote:
> > > On Sat, Feb 21, 2026 at 5:40 PM Vernon Yang <vernon2gm@xxxxxxxxx> wrote:
> > > >
> > > > From: Vernon Yang <yanglincheng@xxxxxxxxxx>
> > > >
> > > > For example, create three task: hot1 -> cold -> hot2. After all three
> > > > task are created, each allocate memory 128MB. the hot1/hot2 task
> > > > continuously access 128 MB memory, while the cold task only accesses
> > > > its memory briefly and then call madvise(MADV_FREE). However, khugepaged
> > > > still prioritizes scanning the cold task and only scans the hot2 task
> > > > after completing the scan of the cold task.
> > > >
> > > > And if all folios in VM_DROPPABLE are lazyfree, Collapsing maintains
            ^^
here

> > > > that property, so we can just collapse and memory pressure in the future
> > >
> > > I don’t think this is accurate. A VMA without VM_DROPPABLE
> > > can still have all folios marked as lazyfree. Therefore, having
> > > all folios lazyfree is not the reason why collapsing preserves
> > > the property.
> >
> > In folio_add_new_anon_rmap(), we know that the vma has the VM_DROPPABLE
> > attribute, which is the root reason why Collapsing maintains that property.
> > The above commit log clearly states "all folios in VM_DROPPABLE are lazyfree"
> >                                                 ^^^^^^^^^^^^^^^
> > (the "if" is redundant and should be removed), not "all folios are lazyfree".
>
> Yes, we should remove the if; otherwise, it’s misleading.
>
> [...]
>
> > >
> > > I would prefer to add a comment about VM_DROPPABLE here
> > > rather than only mentioning it in the changelog.
> >
> > Is the following comment clear?
> >
> > /*
> >  * If the vma has the VM_DROPPABLE flag, the collapse will
> >  * preserve the lazyfree property without needing to skip.
> >  */
>
> Looks good to me.

Hi Andrew, could you please squash the following fix into this patch?
also remove "if" in the changelog above.

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