From: kanoj@google.engr.sgi.com (Kanoj Sarcar)
To: masp0008@stud.uni-sb.de
Cc: linux-mm@kvack.org
Subject: Re: active_mm & SMP & TLB flush: possible bug
Date: Wed, 28 Jul 1999 11:07:30 -0700 (PDT) [thread overview]
Message-ID: <199907281807.LAA14534@google.engr.sgi.com> (raw)
In-Reply-To: <379EF7D0.375C78A4@colorfullife.com> from "Manfred Spraul" at Jul 28, 99 02:30:08 pm
> BTW, where can I find more details about the active_mm implementation?
> specifically, I'd like to know why active_mm was added to
> "struct task_struct".
That goes for a lot of other changes in 2.3 - unfortunately, there
seems to be no concept of release notes etc, that provide one liner
descriptions of the changes being put into a release.
In this case at least, the concept of "active_mm" reduces tlb flushes
when switching *to* a kernel thread, since a kernel thread has no
user level translations, and can use the kernel-level translations
of the previous thread. set_mmu_context updates the task.cr3, which
is checked in __switch_to, and since the cr3 update is skipped, the
tlb's are not flushed.
> >From my first impression, it's a CPU specific information
> (every CPU has exactly one active_mm, threads which are not running have
> no
> active_mm), so I'd have used a global array[NR_CPUS].
Umm, really? My reading of the code was that all kernel threads and
exitted user threads had no "mm", and had an "active_mm" only while
executing on the cpu. Other user threads with user level translations
always have an "mm" and "active_mm".
Kanoj
>
>
> Manfred
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next prev parent reply other threads:[~1999-07-28 18:07 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
1999-07-28 12:30 active_mm & SMP & TLB flush: possible bug Manfred Spraul
1999-07-28 15:46 ` Benjamin C.R. LaHaise
1999-07-28 18:07 ` Kanoj Sarcar [this message]
-- strict thread matches above, loose matches on Subject: below --
1999-07-28 16:58 Manfred Spraul
1999-07-28 18:35 Manfred Spraul, Benjamin C.R. LaHaise
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