On Thu, Dec 9, 2010 at 10:11 PM, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Wednesday, December 8, 2010, Michel Lespinasse <walken@xxxxxxxxxx> wrote:
>>
>> Yes, patch 1/6 changes the long hold time to be in read mode instead
>> of write mode, which is only a band-aid. But, this prepares for patch
>> 5/6, which releases mmap_sem whenever there is contention on it or
>> when blocking on disk reads.
>
> I have to say that I'm not a huge fan of that horribly kludgy
> contention check case.
>
> The "move page-in to read-locked sequence" and the changes to
> get_user_pages look fine, but the contention thing is just disgusting.
> I'd really like to see some other approach if at all possible.
Andrew, should I amend my patches to remove the rwsem_is_contended() code ?
This would involve:
- remove rwsem-implement-rwsem_is_contended.patch and
x86-rwsem-more-precise-rwsem_is_contended-implementation.patch
- in mlock-do-not-hold-mmap_sem-for-extended-periods-of-time.patch,
drop the one hunk making use of rwsem_is_contended (rest of the patch
would still work without it)
- optionally, follow up patch to limit batch size to a constant
in do_mlock_pages():
diff --git a/mm/mlock.c b/mm/mlock.c
index 569ae6a..a505a7e 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -457,15 +457,23 @@ static int do_mlock_pages(unsigned long start, size_t len)
continue;
if (nstart < vma->vm_start)
nstart = vma->vm_start;
+ /*
+ * Constrain batch size to limit mmap_sem hold time.
+ */
+ if (nend > nstart + 1024 * PAGE_SIZE)
+ nend = nstart + 1024 * PAGE_SIZE;
/*
* Now fault in a range of pages. __mlock_vma_pages_range()
* double checks the vma flags, so that it won't mlock pages
* if the vma was already munlocked.
*/
ret = __mlock_vma_pages_range(vma, nstart, nend, &locked);
if (ret < 0) {
ret = __mlock_posix_error_return(ret);
break;
+ } else if (locked) {
+ locked = 0;
+ up_read(&mm->mmap_sem);
}
nend = nstart + ret * PAGE_SIZE;
ret = 0;
I don't really prefer using a constant, but I'm not sure how else to make
Linus happy :)
--
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.
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