From: Jason Gunthorpe <jgg@nvidia.com>
To: Alistair Popple <apopple@nvidia.com>
Cc: linux-mm@kvack.org, akpm@linux-foundation.org,
linux-kernel@vger.kernel.org, "Sierra Guiza,
Alejandro (Alex)" <alex.sierra@amd.com>,
Chaitanya Kulkarni <kch@nvidia.com>,
Dan Williams <dan.j.williams@intel.com>,
Felix Kuehling <Felix.Kuehling@amd.com>,
John Hubbard <jhubbard@nvidia.com>,
Logan Gunthorpe <logang@deltatee.com>,
Miaohe Lin <linmiaohe@huawei.com>,
Muchun Song <songmuchun@bytedance.com>,
Ralph Campbell <rcampbell@nvidia.com>,
David Hildenbrand <david@redhat.com>,
Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH v4 2/2] mm/gup.c: Refactor check_and_migrate_movable_pages()
Date: Mon, 15 Aug 2022 13:15:55 -0300 [thread overview]
Message-ID: <YvpxOyrDBUHagpC6@nvidia.com> (raw)
In-Reply-To: <6b61e9bf7c65f78524db32ba3e65a7eb6b8a76a0.1660269441.git-series.apopple@nvidia.com>
On Fri, Aug 12, 2022 at 12:13:09PM +1000, Alistair Popple wrote:
> When pinning pages with FOLL_LONGTERM check_and_migrate_movable_pages()
> is called to migrate pages out of zones which should not contain any
> longterm pinned pages.
>
> When migration succeeds all pages will have been unpinned so pinning
> needs to be retried. Migration can also fail, in which case the pages
> will also have been unpinned but the operation should not be retried. If
> all pages are in the correct zone nothing will be unpinned and no retry
> is required.
>
> The logic in check_and_migrate_movable_pages() tracks unnecessary state
> and the return codes for each case are difficult to follow. Refactor the
> code to clean this up. No behaviour change is intended.
>
> Signed-off-by: Alistair Popple <apopple@nvidia.com>
>
> ---
This seems like the cleanest version yet!
> +static long check_and_migrate_movable_pages(unsigned long nr_pages,
> + struct page **pages)
> +{
> + int ret;
> + unsigned long collected;
> + LIST_HEAD(movable_page_list);
> +
> + collected = collect_longterm_unpinnable_pages(&movable_page_list, nr_pages, pages);
> + if (!collected)
> + return 0;
> +
> + ret = migrate_longterm_unpinnable_pages(&movable_page_list, nr_pages, pages);
> + if (!ret)
> + return -EAGAIN;
> + else
> + return ret;
I would drop the else path and just return zero
Arguably migrate_longterm_unpinnable_pages() should do the same?
> @@ -2051,10 +2079,10 @@ static long __gup_longterm_locked(struct mm_struct *mm,
> break;
>
> rc = check_and_migrate_movable_pages(rc, pages);
> - } while (!rc);
> + } while (rc == -EAGAIN);
Since the only reader only cares about errno or not errno..
But no biggie either way
Thanks,
Jason
next prev parent reply other threads:[~2022-08-15 16:17 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-12 2:13 [PATCH v4 1/2] mm/gup.c: Don't pass gup_flags to check_and_migrate_movable_pages() Alistair Popple
2022-08-12 2:13 ` [PATCH v4 2/2] mm/gup.c: Refactor check_and_migrate_movable_pages() Alistair Popple
2022-08-12 7:05 ` John Hubbard
2022-08-15 16:15 ` Jason Gunthorpe [this message]
2022-08-16 5:29 ` Alistair Popple
2022-08-16 11:29 ` Jason Gunthorpe
2022-08-17 2:01 ` Alistair Popple
2022-08-17 12:09 ` Jason Gunthorpe
2022-08-17 20:35 ` John Hubbard
2022-08-17 22:50 ` Jason Gunthorpe
2022-08-17 23:05 ` John Hubbard
2022-08-17 23:24 ` Alistair Popple
2022-08-17 23:40 ` Jason Gunthorpe
2022-08-12 12:57 ` [PATCH v4 1/2] mm/gup.c: Don't pass gup_flags to check_and_migrate_movable_pages() Matthew Wilcox
2022-08-12 18:02 ` John Hubbard
2022-08-12 18:11 ` Matthew Wilcox
2022-08-15 5:52 ` Alistair Popple
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