linux-kernel - Re: [RFC] iommu: Use put_pages

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Date:   Thu, 14 Oct 2021 17:32:17 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Robin Murphy <robin.murphy@....com>
Cc:     John Garry <john.garry@...wei.com>, Joerg Roedel <joro@...tes.org>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        Will Deacon <will@...nel.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] iommu: Use put_pages_list

On Thu, Oct 14, 2021 at 05:17:18PM +0100, Robin Murphy wrote:
> On 2021-10-14 12:52, John Garry wrote:
> > On 14/10/2021 12:20, Matthew Wilcox wrote:
> > > I'm going to keep pinging this patch weekly.
> > > 
> > > On Thu, Oct 07, 2021 at 07:17:02PM +0100, Matthew Wilcox wrote:
> > > > ping?
> > 
> > Robin, Were you checking this? You mentioned "I got
> > side-tracked trying to make io-pgtable use that freelist properly" in
> > another thread, which seems related.
> 
> Ooh, thanks for the heads-up John - I'm still only just starting to catch up
> on my mailing list folders since I got back off holiday.
> 
> Indeed I already started untangling the freelist handling in the flush queue
> code (to make the move into iommu-dma smaller). Once I'd figured out how it
> worked I did wonder whether there was any more "standard" field to borrow,
> since page->freelist did seem very much in the minority. If page->lru is it
> then great! From a quick skim of the patch I think I'd only have a few
> trivial review comments to make - certainly no objection to the fundamental
> change itself (indeed I hit a point in io-pgtable-arm where adding to the
> pointer chain got rather awkward, so having proper lists to splice would be
> lovely).

Great to hear!

> Matthew - is this something getting in the way of mm development, or just a
> nice cleanup? I'd be happy either to pursue merging it on its own, or to
> pick it up and work it into a series with my stuff.

This is probably going to get in the way of MM development in ~6 months
time.  I'm happy for you to pick it up and put it in a series of your own!
BTW, the optimisation of the implementation of put_pages_list() is sitting
in akpm's tree, so if you see a performance problem, please give that
a try.