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Date:   Tue, 11 Jul 2023 22:59:52 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Luis Chamberlain <mcgrof@kernel.org>
Cc:     David Hildenbrand <david@redhat.com>,
        Ryan Roberts <ryan.roberts@arm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Yin Fengwei <fengwei.yin@intel.com>,
        Yu Zhao <yuzhao@google.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Anshuman Khandual <anshuman.khandual@arm.com>,
        Yang Shi <shy828301@gmail.com>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [PATCH v2 0/5] variable-order, large folios for anonymous memory
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References: <20230703135330.1865927-1-ryan.roberts@arm.com>
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On Tue, Jul 11, 2023 at 02:11:19PM -0700, Luis Chamberlain wrote:
> On Fri, Jul 07, 2023 at 02:12:01PM +0100, Matthew Wilcox wrote:
> > On Fri, Jul 07, 2023 at 01:40:53PM +0200, David Hildenbrand wrote:
> > 
> > > Is swapping working as expected? zswap?
> > 
> > Suboptimally.  Swap will split folios in order to swap them.
> 
> Wouldn't that mean if high order folios are used a lot but swap is also
> used, until this is fixed you wouldn't get the expected reclaim gains
> for high order folios and we'd need compaction more then?

They're split in shrink_folio_list(), so they stay intact until
that point?

> > Somebody needs to fix that, but it should work.
> 
> As we look at shmem stuff it was on the path so something we have
> considered doing. Ie, it's on our team's list of items to help with
> but currently on a backburner.

Something I was thinking about is that you'll need to prohibit swap
devices or swap files being created on large block devices.  Until
we rewrite the entire swap subsystem ...