Messages in this thread | | | Date | Mon, 21 Nov 2011 15:10:39 -0800 | Subject | Re: [PATCH] ksm: use FAULT_FLAG_ALLOW_RETRY in breaking COW | From | Michel Lespinasse <> |
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On Sat, Nov 19, 2011 at 3:50 AM, Hillf Danton <dhillf@gmail.com> wrote: > The flag, FAULT_FLAG_ALLOW_RETRY, was introduced by the patch, > > mm: retry page fault when blocking on disk transfer > commit: d065bd810b6deb67d4897a14bfe21f8eb526ba99 > > for reducing mmap_sem hold times that are caused by waiting for disk > transfers when accessing file mapped VMAs. > > To break COW, handle_mm_fault() is repeated with mmap_sem held, where > the introduced flag could be used again. > > The straight way is to add changes in break_ksm(), but the function could be > under write-mode mmap_sem, so it has to be dupilcated. > > Signed-off-by: Hillf Danton <dhillf@gmail.com>
I have to concur with Hugh here - FAULT_FLAG_ALLOW_RETRY was introduced to avoid holding mmap_sem while we block on a disk read, but you shouldn't hit this case in the break COW case, so there seems to be little point in adding the flag there.
-- Michel "Walken" Lespinasse A program is never fully debugged until the last user dies. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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