RE: [PATCH v7 4/8] mm: zswap: Refactor code to delete stored offsets in case of errors.

[Sridhar, Kanchana P]

> -----Original Message-----
> From: Nhat Pham <nphamcs@xxxxxxxxx>
> Sent: Tuesday, September 24, 2024 10:25 AM
> To: Sridhar, Kanchana P <kanchana.p.sridhar@xxxxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx;
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> Zou, Nanhai <nanhai.zou@xxxxxxxxx>; Feghali, Wajdi K
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> Subject: Re: [PATCH v7 4/8] mm: zswap: Refactor code to delete stored
> offsets in case of errors.
> 
> On Mon, Sep 23, 2024 at 6:17 PM Kanchana P Sridhar
> <kanchana.p.sridhar@xxxxxxxxx> wrote:
> >
> > Added a new procedure zswap_delete_stored_offsets() that can be
> > called to delete stored offsets in a folio in case zswap_store()
> > fails or zswap is disabled.
> >
> > Refactored the code in zswap_store() that handles these cases,
> > to call zswap_delete_stored_offsets().
> >
> > Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@xxxxxxxxx>
> > ---
> >  mm/zswap.c | 33 ++++++++++++++++++++++++++++++---
> >  1 file changed, 30 insertions(+), 3 deletions(-)
> >
> > diff --git a/mm/zswap.c b/mm/zswap.c
> > index fd35a81b6e36..9bea948d653e 100644
> > --- a/mm/zswap.c
> > +++ b/mm/zswap.c
> > @@ -1435,8 +1435,37 @@ static bool zswap_store_entry(struct xarray
> *tree,
> >         return true;
> >  }
> >
> > +/*
> > + * If the zswap store fails or zswap is disabled, we must invalidate the
> > + * possibly stale entries which were previously stored at the offsets
> > + * corresponding to each page of the folio. Otherwise, writeback could
> > + * overwrite the new data in the swapfile.
> > + *
> > + * This is called after the store of an offset in a large folio has failed.
> 
> "store of a subpage" rather than "stored of an offset"?

Sure, I will make this change in v8.

> 
> 
> > + * All zswap entries in the folio must be deleted. This helps make sure
> > + * that a swapped-out mTHP is either entirely stored in zswap, or entirely
> > + * not stored in zswap.
> > + *
> > + * This is also called if zswap_store() is invoked, but zswap is not enabled.
> > + * All offsets for the folio are deleted from zswap in this case.
> > + */
> > +static void zswap_delete_stored_offsets(struct xarray *tree,
> > +                                       pgoff_t offset,
> > +                                       long nr_pages)
> > +{
> > +       struct zswap_entry *entry;
> > +       long i;
> > +
> > +       for (i = 0; i < nr_pages; ++i) {
> > +               entry = xa_erase(tree, offset + i);
> > +               if (entry)
> > +                       zswap_entry_free(entry);
> > +       }
> > +}
> > +