From: Barry Song <21cnbao@gmail.com>
To: Chris Li <chrisl@kernel.org>
Cc: David Hildenbrand <david@redhat.com>,
ryan.roberts@arm.com, akpm@linux-foundation.org,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
mhocko@suse.com, shy828301@gmail.com,
wangkefeng.wang@huawei.com, willy@infradead.org,
xiang@kernel.org, ying.huang@intel.com, yuzhao@google.com,
surenb@google.com, steven.price@arm.com,
Barry Song <v-songbaohua@oppo.com>,
Chuanhua Han <hanchuanhua@oppo.com>
Subject: Re: [PATCH RFC 5/6] mm: rmap: weaken the WARN_ON in __folio_add_anon_rmap()
Date: Mon, 26 Feb 2024 18:05:43 +1300 [thread overview]
Message-ID: <CAGsJ_4wanQr8mniGnJrzDHKGzWt8J2vT_Mx65+46=qk-R0iM3w@mail.gmail.com> (raw)
In-Reply-To: <CAF8kJuMmh06rCXuiu5V0BiT8t1ckEEnY4rM-ivRBQ+xdyMhRKQ@mail.gmail.com>
On Tue, Jan 30, 2024 at 5:32 AM Chris Li <chrisl@kernel.org> wrote:
>
> On Mon, Jan 29, 2024 at 2:07 AM David Hildenbrand <david@redhat.com> wrote:
> >
> > On 29.01.24 04:25, Chris Li wrote:
> > > Hi David and Barry,
> > >
> > > On Mon, Jan 22, 2024 at 10:49 PM Barry Song <21cnbao@gmail.com> wrote:
> > >>
> > >>>
> > >>>
> > >>> I have on my todo list to move all that !anon handling out of
> > >>> folio_add_anon_rmap_ptes(), and instead make swapin code call add
> > >>> folio_add_new_anon_rmap(), where we'll have to pass an exclusive flag
> > >>> then (-> whole new folio exclusive).
> > >>>
> > >>> That's the cleaner approach.
> > >>>
> > >>
> > >> one tricky thing is that sometimes it is hard to know who is the first
> > >> one to add rmap and thus should
> > >> call folio_add_new_anon_rmap.
> > >> especially when we want to support swapin_readahead(), the one who
> > >> allocated large filio might not
> > >> be that one who firstly does rmap.
> > >
> > > I think Barry has a point. Two tasks might race to swap in the folio
> > > then race to perform the rmap.
> > > folio_add_new_anon_rmap() should only call a folio that is absolutely
> > > "new", not shared. The sharing in swap cache disqualifies that
> > > condition.
> >
> > We have to hold the folio lock. So only one task at a time might do the
> > folio_add_anon_rmap_ptes() right now, and the
> > folio_add_new_shared_anon_rmap() in the future [below].
> >
>
> Ah, I see. The folio_lock() is the answer I am looking for.
>
> > Also observe how folio_add_anon_rmap_ptes() states that one must hold
> > the page lock, because otherwise this would all be completely racy.
> >
> > From the pte swp exclusive flags, we know for sure whether we are
> > dealing with exclusive vs. shared. I think patch #6 does not properly
> > check that all entries are actually the same in that regard (all
> > exclusive vs all shared). That likely needs fixing.
> >
> > [I have converting per-page PageAnonExclusive flags to a single
> > per-folio flag on my todo list. I suspect that we'll keep the
> > per-swp-pte exlusive bits, but the question is rather what we can
> > actually make work, because swap and migration just make it much more
> > complicated. Anyhow, future work]
> >
> > >
> > >> is it an acceptable way to do the below in do_swap_page?
> > >> if (!folio_test_anon(folio))
> > >> folio_add_new_anon_rmap()
> > >> else
> > >> folio_add_anon_rmap_ptes()
> > >
> > > I am curious to know the answer as well.
> >
> >
> > Yes, the end code should likely be something like:
> >
> > /* ksm created a completely new copy */
> > if (unlikely(folio != swapcache && swapcache)) {
> > folio_add_new_anon_rmap(folio, vma, vmf->address);
> > folio_add_lru_vma(folio, vma);
> > } else if (folio_test_anon(folio)) {
> > folio_add_anon_rmap_ptes(rmap_flags)
> > } else {
> > folio_add_new_anon_rmap(rmap_flags)
> > }
> >
> > Maybe we want to avoid teaching all existing folio_add_new_anon_rmap()
> > callers about a new flag, and just have a new
> > folio_add_new_shared_anon_rmap() instead. TBD.
if we have to add a wrapper like folio_add_new_shared_anon_rmap()
to avoid "if (folio_test_anon(folio))" and "else" everywhere, why not
we just do it in folio_add_anon_rmap_ptes() ?
folio_add_anon_rmap_ptes()
{
if (!folio_test_anon(folio))
return folio_add_new_anon_rmap();
}
Anyway, I am going to change the patch 4/6 to if(folio_test_anon)/else first
and drop this 5/6.
we may figure out if we need a wrapper later.
>
> There is more than one caller needed to perform that dance around
> folio_test_anon() then decide which function to call. It would be nice
> to have a wrapper function folio_add_new_shared_anon_rmap() to
> abstract this behavior.
>
>
> >
> > >
> > > BTW, that test might have a race as well. By the time the task got
> > > !anon result, this result might get changed by another task. We need
> > > to make sure in the caller context this race can't happen. Otherwise
> > > we can't do the above safely.
> > Again, folio lock. Observe the folio_lock_or_retry() call that covers
> > our existing folio_add_new_anon_rmap/folio_add_anon_rmap_pte calls.
>
> Ack. Thanks for the explanation.
>
> Chris
Thanks
Barry
next prev parent reply other threads:[~2024-02-26 5:05 UTC|newest]
Thread overview: 116+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-25 14:45 [PATCH v3 0/4] Swap-out small-sized THP without splitting Ryan Roberts
2023-10-25 14:45 ` [PATCH v3 1/4] mm: swap: Remove CLUSTER_FLAG_HUGE from swap_cluster_info:flags Ryan Roberts
2024-02-22 10:19 ` David Hildenbrand
2024-02-22 10:20 ` David Hildenbrand
2024-02-26 17:41 ` Ryan Roberts
2024-02-27 17:10 ` Ryan Roberts
2024-02-27 19:17 ` David Hildenbrand
2024-02-28 9:37 ` Ryan Roberts
2024-02-28 12:12 ` David Hildenbrand
2024-02-28 14:57 ` Ryan Roberts
2024-02-28 15:12 ` David Hildenbrand
2024-02-28 15:18 ` Ryan Roberts
2024-03-01 16:27 ` Ryan Roberts
2024-03-01 16:31 ` Matthew Wilcox
2024-03-01 16:44 ` Ryan Roberts
2024-03-01 17:00 ` David Hildenbrand
2024-03-01 17:14 ` Ryan Roberts
2024-03-01 17:18 ` David Hildenbrand
2024-03-01 17:06 ` Ryan Roberts
2024-03-04 4:52 ` Barry Song
2024-03-04 5:42 ` Barry Song
2024-03-05 7:41 ` Ryan Roberts
2024-03-01 16:31 ` Ryan Roberts
2024-03-01 16:32 ` David Hildenbrand
2024-03-04 16:03 ` Ryan Roberts
2024-03-04 17:30 ` David Hildenbrand
2024-03-04 18:38 ` Ryan Roberts
2024-03-04 20:50 ` David Hildenbrand
2024-03-04 21:55 ` Ryan Roberts
2024-03-04 22:02 ` David Hildenbrand
2024-03-04 22:34 ` Ryan Roberts
2024-03-05 6:11 ` Huang, Ying
2024-03-05 8:35 ` David Hildenbrand
2024-03-05 8:46 ` Ryan Roberts
2024-02-28 13:33 ` Matthew Wilcox
2024-02-28 14:24 ` Ryan Roberts
2024-02-28 14:59 ` Ryan Roberts
2023-10-25 14:45 ` [PATCH v3 2/4] mm: swap: Remove struct percpu_cluster Ryan Roberts
2023-10-25 14:45 ` [PATCH v3 3/4] mm: swap: Simplify ssd behavior when scanner steals entry Ryan Roberts
2023-10-25 14:45 ` [PATCH v3 4/4] mm: swap: Swap-out small-sized THP without splitting Ryan Roberts
2023-10-30 8:18 ` Huang, Ying
2023-10-30 13:59 ` Ryan Roberts
2023-10-31 8:12 ` Huang, Ying
2023-11-03 11:42 ` Ryan Roberts
2023-11-02 7:40 ` Barry Song
2023-11-02 10:21 ` Ryan Roberts
2023-11-02 22:36 ` Barry Song
2023-11-03 11:31 ` Ryan Roberts
2023-11-03 13:57 ` Steven Price
2023-11-04 9:34 ` Barry Song
2023-11-06 10:12 ` Steven Price
2023-11-06 21:39 ` Barry Song
2023-11-08 11:51 ` Steven Price
2023-11-07 12:46 ` Ryan Roberts
2023-11-07 18:05 ` Barry Song
2023-11-08 11:23 ` Barry Song
2023-11-08 20:20 ` Ryan Roberts
2023-11-08 21:04 ` Barry Song
2023-11-04 5:49 ` Barry Song
2024-02-05 9:51 ` Barry Song
2024-02-05 12:14 ` Ryan Roberts
2024-02-18 23:40 ` Barry Song
2024-02-20 20:03 ` Ryan Roberts
2024-03-05 9:00 ` Ryan Roberts
2024-03-05 9:54 ` Barry Song
2024-03-05 10:44 ` Ryan Roberts
2024-02-27 12:28 ` Ryan Roberts
2024-02-27 13:37 ` Ryan Roberts
2024-02-28 2:46 ` Barry Song
2024-02-22 7:05 ` Barry Song
2024-02-22 10:09 ` David Hildenbrand
2024-02-23 9:46 ` Barry Song
2024-02-27 12:05 ` Ryan Roberts
2024-02-28 1:23 ` Barry Song
2024-02-28 9:34 ` David Hildenbrand
2024-02-28 23:18 ` Barry Song
2024-02-28 15:57 ` Ryan Roberts
2023-11-29 7:47 ` [PATCH v3 0/4] " Barry Song
2023-11-29 12:06 ` Ryan Roberts
2023-11-29 20:38 ` Barry Song
2024-01-18 11:10 ` [PATCH RFC 0/6] mm: support large folios swap-in Barry Song
2024-01-18 11:10 ` [PATCH RFC 1/6] arm64: mm: swap: support THP_SWAP on hardware with MTE Barry Song
2024-01-26 23:14 ` Chris Li
2024-02-26 2:59 ` Barry Song
2024-01-18 11:10 ` [PATCH RFC 2/6] mm: swap: introduce swap_nr_free() for batched swap_free() Barry Song
2024-01-26 23:17 ` Chris Li
2024-02-26 4:47 ` Barry Song
2024-01-18 11:10 ` [PATCH RFC 3/6] mm: swap: make should_try_to_free_swap() support large-folio Barry Song
2024-01-26 23:22 ` Chris Li
2024-01-18 11:10 ` [PATCH RFC 4/6] mm: support large folios swapin as a whole Barry Song
2024-01-27 19:53 ` Chris Li
2024-02-26 7:29 ` Barry Song
2024-01-27 20:06 ` Chris Li
2024-02-26 7:31 ` Barry Song
2024-01-18 11:10 ` [PATCH RFC 5/6] mm: rmap: weaken the WARN_ON in __folio_add_anon_rmap() Barry Song
2024-01-18 11:54 ` David Hildenbrand
2024-01-23 6:49 ` Barry Song
2024-01-29 3:25 ` Chris Li
2024-01-29 10:06 ` David Hildenbrand
2024-01-29 16:31 ` Chris Li
2024-02-26 5:05 ` Barry Song [this message]
2024-04-06 23:27 ` Barry Song
2024-01-27 23:41 ` Chris Li
2024-01-18 11:10 ` [PATCH RFC 6/6] mm: madvise: don't split mTHP for MADV_PAGEOUT Barry Song
2024-01-29 2:15 ` Chris Li
2024-02-26 6:39 ` Barry Song
2024-02-27 12:22 ` Ryan Roberts
2024-02-27 22:39 ` Barry Song
2024-02-27 14:40 ` Ryan Roberts
2024-02-27 18:57 ` Barry Song
2024-02-28 3:49 ` Barry Song
2024-01-18 15:25 ` [PATCH RFC 0/6] mm: support large folios swap-in Ryan Roberts
2024-01-18 23:54 ` Barry Song
2024-01-19 13:25 ` Ryan Roberts
2024-01-27 14:27 ` Barry Song
2024-01-29 9:05 ` Huang, Ying
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