From: "Stephen C. Tweedie" <sct@redhat.com>
To: Kanoj Sarcar <kanoj@google.engr.sgi.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.rutgers.edu,
Stephen Tweedie <sct@redhat.com>
Subject: Re: [RFT] [PATCH] kanoj-mm1-2.2.5 ia32 big memory patch
Date: Tue, 11 May 1999 00:41:32 +0100 (BST) [thread overview]
Message-ID: <14135.28332.780955.729082@dukat.scot.redhat.com> (raw)
In-Reply-To: <199905101734.KAA43772@google.engr.sgi.com>
Hi,
On Mon, 10 May 1999 10:33:59 -0700 (PDT), kanoj@google.engr.sgi.com
(Kanoj Sarcar) said:
> There are probably a lot of problems with the code as it stands
> today. Reviewers, please let me know of any possible improvements.
> Any ideas on how to improve the uaccess performance will also be
> greatly appreciated. Testers, your input will be most valuable.
On a first scan one thing in particular jumped out:
+/*
+ * validate in a user page, so that the kernel can use the kernel direct
+ * mapped vaddr for the physical page to access user data. This locking
+ * relies on the fact that the caller has kernel_lock held, which restricts
+ * kswapd (or anyone else looking for a free page) from running and stealing
+ * pages. By the same token, grabbing mmap_sem is not needed.
+ */
Unfortunately, mmap_sem _is_ needed here. Both find_extend_vma and
handle_mm_fault need it. You can't modify or block while scanning the
vma list without it, or you risk breaking things in threaded
applications (for example, taking a page fault in handle_mm_fault
without it can be nasty if you are in the middle of a munmap at the
time).
--Stephen
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next prev parent reply other threads:[~1999-05-10 23:42 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
1999-05-10 17:33 Kanoj Sarcar
1999-05-10 23:41 ` Stephen C. Tweedie [this message]
1999-05-11 0:10 ` Kanoj Sarcar
1999-05-11 0:16 ` Stephen C. Tweedie
1999-05-12 3:19 ` Kanoj Sarcar
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