Pekka Enberg pointed out that double error handlings found after
nilfs_transaction_end() can be avoided by separating abort operation:
OK, I don't understand this. The only way nilfs_transaction_end() can
fail is if we have NILFS_TI_SYNC set and we fail to construct the
segment. But why do we want to construct a segment if we don't commit?
I guess what I'm asking is why don't we have a separate
nilfs_transaction_abort() function that can't fail for the erroneous
case to avoid this double error value tracking thing?
This does the separation and renames nilfs_transaction_end() to
nilfs_transaction_commit() for clarification.
Since, some calls of these functions were used just for exclusion control
against the segment constructor, they are replaced with semaphore
operations.
Acked-by: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This is another patch for fixing the following problems of a memory
copy function in nilfs2 ioctl:
(1) It tries to allocate 128KB size of memory even for small objects.
(2) Though the function repeatedly tries large memory allocations
while reducing the size, GFP_NOWAIT flag is not specified.
This increases the possibility of system memory shortage.
(3) During the retries of (2), verbose warnings are printed
because _GFP_NOWARN flag is not used for the kmalloc calls.
The first patch was still doing large allocations by kmalloc which are
repeatedly tried while reducing the size.
Andi Kleen told me that using copy_from_user for large memory is not
good from the viewpoint of preempt latency:
On Fri, 12 Dec 2008 21:24:11 +0100, Andi Kleen <andi@firstfloor.org> wrote:
> > In the current interface, each data item is copied twice: one is to
> > the allocated memory from user space (via copy_from_user), and another
>
> For such large copies it is better to use multiple smaller (e.g. 4K)
> copy user, that gives better real time preempt latencies. Each cfu has a
> cond_resched(), but only one, not multiple times in the inner loop.
He also advised me that:
On Sun, 14 Dec 2008 16:13:27 +0100, Andi Kleen <andi@firstfloor.org> wrote:
> Better would be if you could go to PAGE_SIZE. order 0 allocations
> are typically the fastest / least likely to stall.
>
> Also in this case it's a good idea to use __get_free_pages()
> directly, kmalloc tends to be become less efficient at larger
> sizes.
For the function in question, the size of buffer memory can be reduced
since the buffer is repeatedly used for a number of small objects. On
the other hand, it may incur large preempt latencies for larger buffer
because a copy_from_user (and a copy_to_user) was applied only once
each cycle.
With that, this revision uses the order 0 allocations with
__get_free_pages() to fix the original problems.
Cc: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This adds userland interface implemented with ioctl.
Signed-off-by: Koji Sato <sato.koji@lab.ntt.co.jp>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
