[RFC PATCH] xfs: support for non-mmu architectures

Octavian Purdila
2015-11-17T22:46:21Z

Naive implementation for non-mmu architectures: allocate physically
contiguous xfs buffers with alloc_pages. Terribly inefficient with
memory and fragmentation on high I/O loads but it may be good enough
for basic usage (which most non-mmu architectures will need).

This patch was tested with lklfuse [1] and basic operations seems to
work even with 16MB allocated for LKL.

[1] https://github.com/lkl/linux

Signed-off-by: Octavian Purdila <octavian.purdila@intel.com>
---
fs/xfs/xfs_buf.c | 27 +++++++++++++++++++++++++++
1 file changed, 27 insertions(+)

diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 8ecffb3..50b5246 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -261,6 +261,7 @@ xfs_buf_free(
ASSERT(list_empty(&bp->b_lru));

if (bp->b_flags & _XBF_PAGES) {
+#ifdef CONFIG_MMU
uint i;

if (xfs_buf_is_vmapped(bp))
@@ -272,6 +273,10 @@ xfs_buf_free(

__free_page(page);
}
+#else
+ free_pages((unsigned long)page_to_virt(bp->b_pages[0]),
+ order_base_2(bp->b_page_count));
+#endif
} else if (bp->b_flags & _XBF_KMEM)
kmem_free(bp->b_addr);
_xfs_buf_free_pages(bp);
@@ -338,7 +343,14 @@ use_alloc_page:
struct page *page;
uint retries = 0;
retry:
+#ifdef CONFIG_MMU
page = alloc_page(gfp_mask);
+#else
+ if (i == 0)
+ page = alloc_pages(gfp_mask, order_base_2(page_count));
+ else
+ page = bp->b_pages[0] + i;
+#endif
if (unlikely(page == NULL)) {
if (flags & XBF_READ_AHEAD) {
bp->b_page_count = i;
@@ -372,8 +384,11 @@ retry:
return 0;

out_free_pages:
+#ifdef CONFIG_MMU
for (i = 0; i < bp->b_page_count; i++)
__free_page(bp->b_pages[i]);
+#endif
+
return error;
}

@@ -392,6 +407,7 @@ _xfs_buf_map_pages(
} else if (flags & XBF_UNMAPPED) {
bp->b_addr = NULL;
} else {
+#ifdef CONFIG_MMU
int retried = 0;
unsigned noio_flag;

@@ -412,6 +428,9 @@ _xfs_buf_map_pages(
vm_unmap_aliases();
} while (retried++ <= 1);
memalloc_noio_restore(noio_flag);
+#else
+ bp->b_addr = page_to_virt(bp->b_pages[0]);
+#endif

if (!bp->b_addr)
return -ENOMEM;
@@ -816,11 +835,19 @@ xfs_buf_get_uncached(
if (error)
goto fail_free_buf;

+#ifdef CONFIG_MMU
for (i = 0; i < page_count; i++) {
bp->b_pages[i] = alloc_page(xb_to_gfp(flags));
if (!bp->b_pages[i])
goto fail_free_mem;
}
+#else
+ bp->b_pages[0] = alloc_pages(flags, order_base_2(page_count));
+ if (!bp->b_pages[0])
+ goto fail_free_buf;
+ for (i = 1; i < page_count; i++)
+ bp->b_pages[i] = bp->b_pages[i-1] + 1;
+#endif
bp->b_flags |= _XBF_PAGES;

error = _xfs_buf_map_pages(bp, 0);
--
1.9.1