Re: [PATCH v2] mm: add lazyfree folio to lru tail

Hailong Liu
2024-08-27T02:29:19Z

On Tue, 27. Aug 14:18, Barry Song wrote:
> On Tue, Aug 27, 2024 at 2:13 PM Hailong Liu <hailong.liu@oppo.com> wrote:
> >
> > On Mon, 26. Aug 09:37, Lokesh Gidra wrote:
> > >
> > > IMHO, within LRU_INACTIVE_FILE, MADV_FREE'ed pages should be
> > > prioritized for reclamation over file ones.
> >
> >
> > > >
> > > > Adding Lokesh.
> > > > Lokesh, could you please comment on the reasoning behind the above
> > > > mentioned change?
> > >
> > > Adding Nicolas as well, in case he wants to add something.
> > IMHO, lruvec_add_folio is enough. if lruvec_add_folio_tail why not use
> > MADV_DONTNEED instead? In MM the reclaim policy prefer to reclaim file cache, if
> > MADV_FREE'd pages directly add to the tail, they might be reclaimed instantly.
> > Also the benefit of workingset_refault_file cannot be convinced for me.
>
> My understanding is that MADV_DONTNEED will immediately free the memory,
> whereas MADV_FREE will release memory only under memory pressure. If
> memory pressure is low, the anonymous memory may still be gotten back
> without causing page faults. This might be what Lokesh is aiming to achieve.
>
Hmm, IIUC, for the reason of watermark, the kswapd would do reclamation without
memory pressure. I worried here is that the madv_free'd pages reclaimed too fast
if add to tail.
> >
> > So we should know the reasons and the benefits of the changes. page faults or ?
> > > >
> > > > >
> > > > > >
> > > > > > --
> > > > > > Michal Hocko
> > > > > > SUSE Labs
> > > > > >
> > > > >
>
> Thanks
> Barry

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