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Date: Wed, 07 Mar 2007 09:04:53 -0800
From: Michael Nishimoto <miken@...mi.com>
To: Christoph Hellwig <hch@....de>
CC: xfs@....sgi.com, ecashin@...aid.com, akpm@...l.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] xfs: stop using kmalloc in xfs_buf_get_noaddr
Incore log buffers are not always a power of two of the page size.
In particular, when xfs is running over software raid devices, the
log buffers are allocated to match the size of a stripe.
However, they are always a multiple of PAGE_SIZE, so we are still safe.
Michael
Christoph Hellwig wrote:
>Currently xfs_buf_get_noaddr allocates memory using kmem_alloc which
>can end up either in kmalloc or vmalloc and assigns it to the buffer.
>This patch changes it to allocate individual pages and if there is
>more then one maps it into kernel virtual space using vmap.
>
>This means the minimum buffer allocation is PAGE_SIZE now. For two
>of the three caller (log buffers, log recovery) that is perfectly
>fine, because they always allocate buffers that are a power of two
>of the page size anyway. For xfs_zero_remaining_bytes the minimum
>allocation goes up from blocksize to pagesize and thus there is
>a potential waste of memory for blocksize < pagesize allocations,
>which is unfortunate but not directly solveable when block
>drivers expect reference countable pages. To fix this waste
>xfs_zero_remaining_bytes could be rewritten to zero more than
>a single block at a time, which sounds like a good idea in general.
>
>
>Signed-off-by: Christoph Hellwig <hch@....de>
>
>Index: linux-2.6/fs/xfs/linux-2.6/xfs_buf.c
>===================================================================
>--- linux-2.6.orig/fs/xfs/linux-2.6/xfs_buf.c 2007-03-05 15:54:40.000000000 +0100
>+++ linux-2.6/fs/xfs/linux-2.6/xfs_buf.c 2007-03-05 15:54:47.000000000 +0100
>@@ -314,7 +314,7 @@
>
> ASSERT(list_empty(&bp->b_hash_list));
>
>- if (bp->b_flags & _XBF_PAGE_CACHE) {
>+ if (bp->b_flags & (_XBF_PAGE_CACHE|_XBF_PAGES)) {
> uint i;
>
> if ((bp->b_flags & XBF_MAPPED) && (bp->b_page_count > 1))
>@@ -323,18 +323,11 @@
> for (i = 0; i < bp->b_page_count; i++) {
> struct page *page = bp->b_pages[i];
>
>- ASSERT(!PagePrivate(page));
>+ if (bp->b_flags & _XBF_PAGE_CACHE)
>+ ASSERT(!PagePrivate(page));
> page_cache_release(page);
> }
> _xfs_buf_free_pages(bp);
>- } else if (bp->b_flags & _XBF_KMEM_ALLOC) {
>- /*
>- * XXX(hch): bp->b_count_desired might be incorrect (see
>- * xfs_buf_associate_memory for details), but fortunately
>- * the Linux version of kmem_free ignores the len argument..
>- */
>- kmem_free(bp->b_addr, bp->b_count_desired);
>- _xfs_buf_free_pages(bp);
> }
>
> xfs_buf_deallocate(bp);
>@@ -764,41 +757,41 @@
> size_t len,
> xfs_buftarg_t *target)
> {
>- size_t malloc_len = len;
>+ unsigned long page_count = PAGE_ALIGN(len) >> PAGE_SHIFT;
>+ int error, i;
> xfs_buf_t *bp;
>- void *data;
>- int error;
>
> bp = xfs_buf_allocate(0);
> if (unlikely(bp == NULL))
> goto fail;
> _xfs_buf_initialize(bp, target, 0, len, 0);
>
>- try_again:
>- data = kmem_alloc(malloc_len, KM_SLEEP | KM_MAYFAIL | KM_LARGE);
>- if (unlikely(data == NULL))
>+ error = _xfs_buf_get_pages(bp, page_count, 0);
>+ if (error)
> goto fail_free_buf;
>
>- /* check whether alignment matches.. */
>- if ((__psunsigned_t)data !=
>- ((__psunsigned_t)data & ~target->bt_smask)) {
>- /* .. else double the size and try again */
>- kmem_free(data, malloc_len);
>- malloc_len <<= 1;
>- goto try_again;
>- }
>-
>- error = xfs_buf_associate_memory(bp, data, len);
>- if (error)
>+ for (i = 0; i < page_count; i++) {
>+ bp->b_pages[i] = alloc_page(GFP_KERNEL);
>+ if (!bp->b_pages[i])
>+ goto fail_free_mem;
>+ }
>+ bp->b_flags |= _XBF_PAGES;
>+
>+ error = _xfs_buf_map_pages(bp, XBF_MAPPED);
>+ if (unlikely(error)) {
>+ printk(KERN_WARNING "%s: failed to map pages\n",
>+ __FUNCTION__);
> goto fail_free_mem;
>- bp->b_flags |= _XBF_KMEM_ALLOC;
>+ }
>
> xfs_buf_unlock(bp);
>
> XB_TRACE(bp, "no_daddr", data);
> return bp;
>+
> fail_free_mem:
>- kmem_free(data, malloc_len);
>+ for ( ; i >= 0; i++)
>+ __free_page(bp->b_pages[i]);
> fail_free_buf:
> xfs_buf_free(bp);
> fail:
>Index: linux-2.6/fs/xfs/linux-2.6/xfs_buf.h
>===================================================================
>--- linux-2.6.orig/fs/xfs/linux-2.6/xfs_buf.h 2007-03-05 15:54:40.000000000 +0100
>+++ linux-2.6/fs/xfs/linux-2.6/xfs_buf.h 2007-03-05 15:55:06.000000000 +0100
>@@ -63,7 +63,7 @@
>
> /* flags used only internally */
> _XBF_PAGE_CACHE = (1 << 17),/* backed by pagecache */
>- _XBF_KMEM_ALLOC = (1 << 18),/* backed by kmem_alloc() */
>+ _XBF_PAGES = (1 << 18), /* backed by refcounted pages */
> _XBF_RUN_QUEUES = (1 << 19),/* run block device task queue */
> _XBF_DELWRI_Q = (1 << 21), /* buffer on delwri queue */
> } xfs_buf_flags_t;
>
>
>
>
-
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