On 6/14/23 15:45, Matthew Wilcox wrote:
On Wed, Jun 14, 2023 at 01:46:32PM +0200, Hannes Reinecke wrote:
/*
- * Each block ramdisk device has a xarray brd_pages of pages that stores
- * the pages containing the block device's contents. A brd page's ->index is
- * its offset in PAGE_SIZE units. This is similar to, but in no way connected
- * with, the kernel's pagecache or buffer cache (which sit above our block
- * device).
+ * Each block ramdisk device has a xarray of folios that stores the folios
+ * containing the block device's contents. A brd folio's ->index is its offset
+ * in PAGE_SIZE units. This is similar to, but in no way connected with,
+ * the kernel's pagecache or buffer cache (which sit above our block device).
Having read my way to the end of the series, I can now circle back and
say this comment is wrong. The folio->index is its offset in PAGE_SIZE
units if the sector size is <= PAGE_SIZE, otherwise it's the offset in
sector size units. This is _different from_ the pagecache which uses
PAGE_SIZE units and multi-index entries in the XArray.
Hmm. I am aware that brd is using the ->index field in a different way,
but I thought I got it straigtened out ...
@@ -144,29 +143,29 @@ static int copy_to_brd_setup(struct brd_device *brd, sector_t sector, size_t n,
static void copy_to_brd(struct brd_device *brd, const void *src,
sector_t sector, size_t n)
{
- struct page *page;
+ struct folio *folio;
void *dst;
unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
size_t copy;
copy = min_t(size_t, n, PAGE_SIZE - offset);
- page = brd_lookup_page(brd, sector);
- BUG_ON(!page);
+ folio = brd_lookup_folio(brd, sector);
+ BUG_ON(!folio);
- dst = kmap_atomic(page);
- memcpy(dst + offset, src, copy);
- kunmap_atomic(dst);
+ dst = kmap_local_folio(folio, offset);
+ memcpy(dst, src, copy);
+ kunmap_local(dst);
This should use memcpy_to_folio(), which doesn't exist yet.
Compile-tested patch incoming shortly ...
Ah. You live and learn.
+ folio = brd_lookup_folio(brd, sector);
+ if (folio) {
+ src = kmap_local_folio(folio, offset);
+ memcpy(dst, src, copy);
+ kunmap_local(src);
And this will need memcpy_from_folio(), patch for that incoming too.
@@ -226,15 +225,15 @@ static int brd_do_bvec(struct brd_device *brd, struct page *page,
goto out;
}
- mem = kmap_atomic(page);
+ mem = kmap_local_folio(folio, off);
if (!op_is_write(opf)) {
- copy_from_brd(mem + off, brd, sector, len);
- flush_dcache_page(page);
+ copy_from_brd(mem, brd, sector, len);
+ flush_dcache_folio(folio);
Nngh. This will need to be a more complex loop. I don't think we can
do a simple abstraction here. Perhaps you can base it on the two
patches you're about to see?
Sure.
Might explain the strange crashes I've seen ...
Cheers,
Hannes
