From: Mel Gorman <mgorman@techsingularity.net>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Nicolas Saenz Julienne <nsaenzju@redhat.com>,
Marcelo Tosatti <mtosatti@redhat.com>,
Michal Hocko <mhocko@kernel.org>, Hugh Dickins <hughd@google.com>,
LKML <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>
Subject: Re: [PATCH 7/7] mm/page_alloc: Replace local_lock with normal spinlock
Date: Tue, 21 Jun 2022 10:26:33 +0100 [thread overview]
Message-ID: <20220621092633.GD15453@techsingularity.net> (raw)
In-Reply-To: <43033655-2e78-621b-cc76-c3dc53024d00@suse.cz>
On Thu, Jun 16, 2022 at 07:01:53PM +0200, Vlastimil Babka wrote:
> On 6/13/22 14:56, Mel Gorman wrote:
> > struct per_cpu_pages is no longer strictly local as PCP lists can be
> > drained remotely using a lock for protection. While the use of local_lock
> > works, it goes against the intent of local_lock which is for "pure
> > CPU local concurrency control mechanisms and not suited for inter-CPU
> > concurrency control" (Documentation/locking/locktypes.rst)
> >
> > local_lock protects against migration between when the percpu pointer is
> > accessed and the pcp->lock acquired. The lock acquisition is a preemption
> > point so in the worst case, a task could migrate to another NUMA node
> > and accidentally allocate remote memory. The main requirement is to pin
> > the task to a CPU that is suitable for PREEMPT_RT and !PREEMPT_RT.
> >
> > Replace local_lock with helpers that pin a task to a CPU, lookup the
> > per-cpu structure and acquire the embedded lock. It's similar to local_lock
> > without breaking the intent behind the API. It is not a complete API
> > as only the parts needed for PCP-alloc are implemented but in theory,
> > the generic helpers could be promoted to a general API if there was
> > demand for an embedded lock within a per-cpu struct with a guarantee
> > that the per-cpu structure locked matches the running CPU and cannot use
> > get_cpu_var due to RT concerns. PCP requires these semantics to avoid
> > accidentally allocating remote memory.
> >
> > Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
>
> ...
>
> > @@ -3367,30 +3429,17 @@ static int nr_pcp_high(struct per_cpu_pages *pcp, struct zone *zone,
> > return min(READ_ONCE(pcp->batch) << 2, high);
> > }
> >
> > -/* Returns true if the page was committed to the per-cpu list. */
> > -static bool free_unref_page_commit(struct page *page, int migratetype,
> > - unsigned int order, bool locked)
> > +static void free_unref_page_commit(struct per_cpu_pages *pcp, struct zone *zone,
> > + struct page *page, int migratetype,
> > + unsigned int order)
>
> Hmm given this drops the "bool locked" and bool return value again, my
> suggestion for patch 5/7 would result in less churn as those woudn't need to
> be introduced?
>
It would. I considered doing exactly that but I didn't want to drop the
reviewed-bys and tested-bys and the change was significant enough to do
that. As multiple fixes are needed, I'll do that.
> ...
>
> > @@ -3794,19 +3805,29 @@ static struct page *rmqueue_pcplist(struct zone *preferred_zone,
> > struct list_head *list;
> > struct page *page;
> > unsigned long flags;
> > + unsigned long __maybe_unused UP_flags;
> >
> > - local_lock_irqsave(&pagesets.lock, flags);
> > + /*
> > + * spin_trylock_irqsave is not necessary right now as it'll only be
> > + * true when contending with a remote drain. It's in place as a
> > + * preparation step before converting pcp locking to spin_trylock
> > + * to protect against IRQ reentry.
> > + */
> > + pcp_trylock_prepare(UP_flags);
> > + pcp = pcp_spin_trylock_irqsave(zone->per_cpu_pageset, flags);
> > + if (!pcp)
>
> Besides the missing unpin Andrew fixed, I think also this is missing
> pcp_trylock_finish(UP_flags); ?
>
Yes.
--
Mel Gorman
SUSE Labs
next prev parent reply other threads:[~2022-06-21 9:26 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-13 12:56 [PATCH v4 00/7] Drain remote per-cpu directly Mel Gorman
2022-06-13 12:56 ` [PATCH 1/7] mm/page_alloc: Add page->buddy_list and page->pcp_list Mel Gorman
2022-06-13 12:56 ` [PATCH 2/7] mm/page_alloc: Use only one PCP list for THP-sized allocations Mel Gorman
2022-06-13 12:56 ` [PATCH 3/7] mm/page_alloc: Split out buddy removal code from rmqueue into separate helper Mel Gorman
2022-06-13 12:56 ` [PATCH 4/7] mm/page_alloc: Remove mistaken page == NULL check in rmqueue Mel Gorman
2022-06-13 12:56 ` [PATCH 5/7] mm/page_alloc: Protect PCP lists with a spinlock Mel Gorman
2022-06-16 15:59 ` Vlastimil Babka
2022-06-13 12:56 ` [PATCH 6/7] mm/page_alloc: Remotely drain per-cpu lists Mel Gorman
2022-06-16 16:41 ` Vlastimil Babka
2022-06-13 12:56 ` [PATCH 7/7] mm/page_alloc: Replace local_lock with normal spinlock Mel Gorman
2022-06-15 22:43 ` Yu Zhao
[not found] ` <CGME20220615224855eucas1p1ea6d90c23ec9423dfe04b267f6dddd2a@eucas1p1.samsung.com>
2022-06-15 22:48 ` Marek Szyprowski
2022-06-15 23:04 ` Andrew Morton
2022-06-16 3:05 ` Yu Zhao
2022-06-17 7:55 ` Vlastimil Babka
2022-06-17 6:47 ` Marek Szyprowski
2022-06-21 9:21 ` Mel Gorman
2022-06-16 17:01 ` Vlastimil Babka
2022-06-16 21:07 ` Yu Zhao
2022-06-17 7:57 ` Vlastimil Babka
2022-06-21 9:27 ` Mel Gorman
2022-06-21 9:26 ` Mel Gorman [this message]
2022-06-17 9:39 ` Nicolas Saenz Julienne
2022-06-21 9:29 ` Mel Gorman
2022-06-21 9:31 ` Nicolas Saenz Julienne
2022-07-03 9:44 ` [mm/page_alloc] 2bd8eec68f: BUG:sleeping_function_called_from_invalid_context_at_mm/gup.c kernel test robot
2022-07-03 20:22 ` Andrew Morton
2022-07-05 13:51 ` Oliver Sang
2022-07-06 9:55 ` Mel Gorman
2022-07-06 11:53 ` Mel Gorman
2022-07-06 14:21 ` Oliver Sang
2022-07-06 14:52 ` Mel Gorman
2022-07-07 8:22 ` Oliver Sang
2022-07-06 14:25 ` Oliver Sang
2022-07-06 14:53 ` Mel Gorman
2022-07-07 21:55 ` Vlastimil Babka
2022-07-08 10:56 ` Mel Gorman
2022-07-12 5:04 ` Oliver Sang
2022-06-24 12:54 [PATCH v5 00/7] Drain remote per-cpu directly Mel Gorman
2022-06-24 12:54 ` [PATCH 7/7] mm/page_alloc: Replace local_lock with normal spinlock Mel Gorman
2022-06-24 18:59 ` Yu Zhao
2022-07-04 14:39 ` Vlastimil Babka
2022-07-04 16:33 ` Nicolas Saenz Julienne
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20220621092633.GD15453@techsingularity.net \
--to=mgorman@techsingularity.net \
--cc=akpm@linux-foundation.org \
--cc=hughd@google.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mhocko@kernel.org \
--cc=mtosatti@redhat.com \
--cc=nsaenzju@redhat.com \
--cc=vbabka@suse.cz \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).