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

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Message-ID: <SJ0PR11MB56781536ABC19E44614131E4C9682@SJ0PR11MB5678.namprd11.prod.outlook.com>
Date: Tue, 24 Sep 2024 20:41:48 +0000
From: "Sridhar, Kanchana P" <kanchana.p.sridhar@...el.com>
To: Nhat Pham <nphamcs@...il.com>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>, "hannes@...xchg.org"
	<hannes@...xchg.org>, "yosryahmed@...gle.com" <yosryahmed@...gle.com>,
	"chengming.zhou@...ux.dev" <chengming.zhou@...ux.dev>,
	"usamaarif642@...il.com" <usamaarif642@...il.com>, "shakeel.butt@...ux.dev"
	<shakeel.butt@...ux.dev>, "ryan.roberts@....com" <ryan.roberts@....com>,
	"Huang, Ying" <ying.huang@...el.com>, "21cnbao@...il.com"
	<21cnbao@...il.com>, "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"Zou, Nanhai" <nanhai.zou@...el.com>, "Feghali, Wajdi K"
	<wajdi.k.feghali@...el.com>, "Gopal, Vinodh" <vinodh.gopal@...el.com>,
	"Sridhar, Kanchana P" <kanchana.p.sridhar@...el.com>
Subject: RE: [PATCH v7 4/8] mm: zswap: Refactor code to delete stored offsets
 in case of errors.

> -----Original Message-----
> From: Nhat Pham <nphamcs@...il.com>
> Sent: Tuesday, September 24, 2024 10:25 AM
> To: Sridhar, Kanchana P <kanchana.p.sridhar@...el.com>
> Cc: linux-kernel@...r.kernel.org; linux-mm@...ck.org;
> hannes@...xchg.org; yosryahmed@...gle.com;
> chengming.zhou@...ux.dev; usamaarif642@...il.com;
> shakeel.butt@...ux.dev; ryan.roberts@....com; Huang, Ying
> <ying.huang@...el.com>; 21cnbao@...il.com; akpm@...ux-foundation.org;
> Zou, Nanhai <nanhai.zou@...el.com>; Feghali, Wajdi K
> <wajdi.k.feghali@...el.com>; Gopal, Vinodh <vinodh.gopal@...el.com>
> 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@...el.com> 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@...el.com>
> > ---
> >  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);
> > +       }
> > +}
> > +