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.
> @@ -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 ...
> + 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?
