From: Peter Zijlstra <peterz@infradead.org>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Rik van Riel <riel@surriel.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Andy Lutomirski <luto@kernel.org>,
LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
Mike Galbraith <efault@gmx.de>, kernel-team <kernel-team@fb.com>,
Ingo Molnar <mingo@kernel.org>,
Dave Hansen <dave.hansen@intel.com>
Subject: Re: [PATCH 4/7] x86,tlb: make lazy TLB mode lazier
Date: Fri, 20 Jul 2018 11:32:39 +0200 [thread overview]
Message-ID: <20180720093239.GO2494@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CALCETrWDiMhgiR3f8n0jdWcW31EDJ+Waq0wh5sMDutfigANGnA@mail.gmail.com>
On Thu, Jul 19, 2018 at 09:45:47AM -0700, Andy Lutomirski wrote:
> After some grepping, there are very few users. The
> only nontrivial ones are the ones in kernel/ and mm/mmu_context.c that
> are involved in the rather complicated dance of refcounting active_mm.
Something like so should work I suppose.
It keeps the field, but ensure that for all tasks tsk->active_mm ==
tsk->mm. The implication is that switch_mm(.prev == NULL) should work
(it does for x86, we don't care about @prev).
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d84eafcf5e29..7bfd850c6bf7 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2780,12 +2780,8 @@ static __always_inline struct rq *
context_switch(struct rq *rq, struct task_struct *prev,
struct task_struct *next, struct rq_flags *rf)
{
- struct mm_struct *mm, *oldmm;
-
prepare_task_switch(rq, prev, next);
- mm = next->mm;
- oldmm = prev->active_mm;
/*
* For paravirt, this is coupled with an exit in switch_to to
* combine the page table reload and the switch backend into
@@ -2800,16 +2796,32 @@ context_switch(struct rq *rq, struct task_struct *prev,
* membarrier after storing to rq->curr, before returning to
* user-space.
*/
- if (!mm) {
- next->active_mm = oldmm;
- mmgrab(oldmm);
- enter_lazy_tlb(oldmm, next);
- } else
- switch_mm_irqs_off(oldmm, mm, next);
-
- if (!prev->mm) {
- prev->active_mm = NULL;
- rq->prev_mm = oldmm;
+
+ /*
+ * kernel -> kernel lazy + transfer active
+ * user -> kernel lazy + mmgrab() active
+ *
+ * kernel -> user switch + mmdrop() active
+ * user -> user switch
+ */
+ if (!next->mm) { // to kernel
+ enter_lazy_tlb(prev->active_mm, next);
+
+#ifdef ARCH_NO_ACTIVE_MM
+ next->active_mm = prev->active_mm;
+ if (prev->mm) // from user
+ mmgrab(prev->active_mm);
+#endif
+ } else { // to user
+ switch_mm_irqs_off(prev->active_mm, next->mm, next);
+
+#ifdef ARCH_NO_ACTIVE_MM
+ if (!prev->mm) { // from kernel
+ /* will mmdrop() in finish_task_switch(). */
+ rq->prev_mm = prev->active_mm;
+ prev->active_mm = NULL;
+ }
+#endif
}
rq->clock_update_flags &= ~(RQCF_ACT_SKIP|RQCF_REQ_SKIP);
diff --git a/mm/mmu_context.c b/mm/mmu_context.c
index 3e612ae748e9..770bb615d115 100644
--- a/mm/mmu_context.c
+++ b/mm/mmu_context.c
@@ -12,6 +12,10 @@
#include <asm/mmu_context.h>
+#ifndef finish_arch_post_lock_switch
+# define finish_arch_post_lock_switch() do { } while (0)
+#endif
+
/*
* use_mm
* Makes the calling kernel thread take on the specified
@@ -33,12 +37,14 @@ void use_mm(struct mm_struct *mm)
tsk->mm = mm;
switch_mm(active_mm, mm, tsk);
task_unlock(tsk);
-#ifdef finish_arch_post_lock_switch
finish_arch_post_lock_switch();
-#endif
+#ifdef ARCH_NO_ACTIVE_MM
+ WARN_ON_ONCE(active_mm != NULL);
+#else
if (active_mm != mm)
mmdrop(active_mm);
+#endif
}
EXPORT_SYMBOL_GPL(use_mm);
@@ -57,8 +63,22 @@ void unuse_mm(struct mm_struct *mm)
task_lock(tsk);
sync_mm_rss(mm);
tsk->mm = NULL;
+
+ WARN_ON_ONCE(tsk->active_mm != mm);
+
+#ifdef ARCH_NO_ACTIVE_MM
+ switch_mm(tsk->active_mm, &init_mm, tsk);
+ mmdrop(tsk->active_mm);
+ tsk->active_mm = NULL;
+#else
/* active_mm is still 'mm' */
enter_lazy_tlb(mm, tsk);
+#endif
+
task_unlock(tsk);
+
+#ifdef ARCH_NO_ACTIVE_MM
+ finish_arch_post_lock_switch();
+#endif
}
EXPORT_SYMBOL_GPL(unuse_mm);
next prev parent reply other threads:[~2018-07-20 9:32 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-16 19:03 [PATCH v6 0/7] x86,tlb,mm: make lazy TLB mode even lazier Rik van Riel
2018-07-16 19:03 ` [PATCH 1/7] mm: allocate mm_cpumask dynamically based on nr_cpu_ids Rik van Riel
2018-07-17 9:33 ` [tip:x86/mm] mm: Allocate the mm_cpumask (mm->cpu_bitmap[]) " tip-bot for Rik van Riel
2018-08-04 22:28 ` [PATCH 1/7] mm: allocate mm_cpumask " Guenter Roeck
2018-07-16 19:03 ` [PATCH 2/7] x86,tlb: leave lazy TLB mode at page table free time Rik van Riel
2018-07-17 9:34 ` [tip:x86/mm] x86/mm/tlb: Leave " tip-bot for Rik van Riel
2018-07-17 11:46 ` Peter Zijlstra
2018-07-25 1:00 ` Anders Roxell
2018-08-16 1:54 ` [PATCH 2/7] x86,tlb: leave " Andy Lutomirski
2018-08-16 5:31 ` Rik van Riel
2018-07-16 19:03 ` [PATCH 3/7] x86,mm: restructure switch_mm_irqs_off Rik van Riel
2018-07-17 9:34 ` [tip:x86/mm] x86/mm/tlb: Restructure switch_mm_irqs_off() tip-bot for Rik van Riel
2018-10-09 14:58 ` tip-bot for Rik van Riel
2018-07-16 19:03 ` [PATCH 4/7] x86,tlb: make lazy TLB mode lazier Rik van Riel
2018-07-17 9:35 ` [tip:x86/mm] x86/mm/tlb: Make " tip-bot for Rik van Riel
2018-07-17 11:33 ` Peter Zijlstra
2018-07-18 15:33 ` Rik van Riel
2018-07-18 16:00 ` Peter Zijlstra
[not found] ` <081E558D-DB34-4A18-A35C-896BC47F6EBA@surriel.com>
2018-07-18 18:23 ` Peter Zijlstra
2018-07-18 18:51 ` Rik van Riel
2018-07-19 9:13 ` Peter Zijlstra
2018-07-17 20:04 ` [PATCH 4/7] x86,tlb: make " Andy Lutomirski
[not found] ` <FF977B78-140F-4787-AA57-0EA934017D85@surriel.com>
2018-07-17 21:29 ` Andy Lutomirski
2018-07-17 22:05 ` Rik van Riel
2018-07-17 22:27 ` Andy Lutomirski
2018-07-18 20:58 ` Rik van Riel
2018-07-18 23:13 ` Andy Lutomirski
[not found] ` <B976CC13-D014-433A-83DE-F8DF9AB4F421@surriel.com>
2018-07-19 16:45 ` Andy Lutomirski
2018-07-19 17:04 ` Andy Lutomirski
2018-07-20 4:57 ` Benjamin Herrenschmidt
2018-07-20 8:30 ` Peter Zijlstra
2018-07-23 12:26 ` Rik van Riel
2018-07-24 16:33 ` Will Deacon
[not found] ` <CF849A07-B7CE-4DE9-8246-53AC5A53A705@surriel.com>
2018-07-19 17:18 ` Andy Lutomirski
2018-07-20 8:02 ` Vitaly Kuznetsov
2018-07-20 9:49 ` Peter Zijlstra
2018-07-20 10:18 ` Vitaly Kuznetsov
2018-07-20 9:32 ` Peter Zijlstra [this message]
2018-07-20 11:04 ` Peter Zijlstra
2018-07-16 19:03 ` [PATCH 5/7] x86,tlb: only send page table free TLB flush to lazy TLB CPUs Rik van Riel
2018-07-17 9:35 ` [tip:x86/mm] x86/mm/tlb: Only " tip-bot for Rik van Riel
2018-07-17 11:39 ` Peter Zijlstra
[not found] ` <1F8BDD25-864D-4105-B872-2109AA417454@surriel.com>
[not found] ` <24AA4367-22A1-450E-8F6A-3CBF39518384@surriel.com>
2018-07-18 16:19 ` Peter Zijlstra
2018-07-16 19:03 ` [PATCH 6/7] x86,mm: always use lazy TLB mode Rik van Riel
2018-07-17 9:36 ` [tip:x86/mm] x86/mm/tlb: Always " tip-bot for Rik van Riel
2018-10-09 14:58 ` tip-bot for Rik van Riel
2018-07-16 19:03 ` [PATCH 7/7] x86,switch_mm: skip atomic operations for init_mm Rik van Riel
2018-07-17 9:36 ` [tip:x86/mm] x86/mm/tlb: Skip atomic operations for 'init_mm' in switch_mm_irqs_off() tip-bot for Rik van Riel
-- strict thread matches above, loose matches on Subject: below --
2018-07-10 14:28 [PATCH v5 0/7] x86,tlb,mm: make lazy TLB mode even lazier Rik van Riel
2018-07-10 14:28 ` [PATCH 4/7] x86,tlb: make lazy TLB mode lazier Rik van Riel
2018-07-06 21:56 [PATCH v4 0/7] x86,tlb,mm: make lazy TLB mode even lazier Rik van Riel
2018-07-06 21:56 ` [PATCH 4/7] x86,tlb: make lazy TLB mode lazier Rik van Riel
2018-06-29 14:29 [PATCH v3 0/7] x86,tlb,mm: make lazy TLB mode even lazier Rik van Riel
2018-06-29 14:29 ` [PATCH 4/7] x86,tlb: make lazy TLB mode lazier Rik van Riel
2018-06-29 17:05 ` Dave Hansen
2018-06-29 17:29 ` Rik van Riel
2018-06-20 19:56 [PATCH 0/7] x86,tlb,mm: make lazy TLB mode even lazier Rik van Riel
2018-06-20 19:56 ` [PATCH 4/7] x86,tlb: make lazy TLB mode lazier Rik van Riel
2018-06-22 15:04 ` Andy Lutomirski
2018-06-22 15:15 ` Rik van Riel
2018-06-22 15:34 ` Andy Lutomirski
2018-06-22 17:05 ` Dave Hansen
2018-06-22 17:16 ` Rik van Riel
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=20180720093239.GO2494@hirez.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=dave.hansen@intel.com \
--cc=efault@gmx.de \
--cc=kernel-team@fb.com \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@amacapital.net \
--cc=luto@kernel.org \
--cc=mingo@kernel.org \
--cc=riel@surriel.com \
--cc=vkuznets@redhat.com \
--cc=x86@kernel.org \
/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).