On Wed, Mar 05, 2025 at 07:05:27AM -0700, Christoph Hellwig wrote:
> The fallback buffer allocation path currently open codes a suboptimal
> version of vmalloc to allocate pages that are then mapped into
> vmalloc space. Switch to using vmalloc instead, which uses all the
> optimizations in the common vmalloc code, and removes the need to
> track the backing pages in the xfs_buf structure.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Looks good now,
Reviewed-by: "Darrick J. Wong" <djwong@xxxxxxxxxx>
--D
> ---
> fs/xfs/xfs_buf.c | 207 ++++++++++---------------------------------
> fs/xfs/xfs_buf.h | 7 --
> fs/xfs/xfs_buf_mem.c | 11 +--
> 3 files changed, 48 insertions(+), 177 deletions(-)
>
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index 2b4b8c104b0c..f28ca5cb5bd8 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -55,13 +55,6 @@ static inline bool xfs_buf_is_uncached(struct xfs_buf *bp)
> return bp->b_rhash_key == XFS_BUF_DADDR_NULL;
> }
>
> -static inline int
> -xfs_buf_vmap_len(
> - struct xfs_buf *bp)
> -{
> - return (bp->b_page_count * PAGE_SIZE);
> -}
> -
> /*
> * When we mark a buffer stale, we remove the buffer from the LRU and clear the
> * b_lru_ref count so that the buffer is freed immediately when the buffer
> @@ -190,29 +183,6 @@ _xfs_buf_alloc(
> return 0;
> }
>
> -static void
> -xfs_buf_free_pages(
> - struct xfs_buf *bp)
> -{
> - uint i;
> -
> - ASSERT(bp->b_flags & _XBF_PAGES);
> -
> - if (is_vmalloc_addr(bp->b_addr))
> - vm_unmap_ram(bp->b_addr, bp->b_page_count);
> -
> - for (i = 0; i < bp->b_page_count; i++) {
> - if (bp->b_pages[i])
> - folio_put(page_folio(bp->b_pages[i]));
> - }
> - mm_account_reclaimed_pages(howmany(BBTOB(bp->b_length), PAGE_SIZE));
> -
> - if (bp->b_pages != bp->b_page_array)
> - kfree(bp->b_pages);
> - bp->b_pages = NULL;
> - bp->b_flags &= ~_XBF_PAGES;
> -}
> -
> static void
> xfs_buf_free_callback(
> struct callback_head *cb)
> @@ -227,16 +197,23 @@ static void
> xfs_buf_free(
> struct xfs_buf *bp)
> {
> + unsigned int size = BBTOB(bp->b_length);
> +
> trace_xfs_buf_free(bp, _RET_IP_);
>
> ASSERT(list_empty(&bp->b_lru));
>
> + if (!xfs_buftarg_is_mem(bp->b_target) && size >= PAGE_SIZE)
> + mm_account_reclaimed_pages(howmany(size, PAGE_SHIFT));
> +
> if (xfs_buftarg_is_mem(bp->b_target))
> xmbuf_unmap_page(bp);
> - else if (bp->b_flags & _XBF_PAGES)
> - xfs_buf_free_pages(bp);
> + else if (is_vmalloc_addr(bp->b_addr))
> + vfree(bp->b_addr);
> else if (bp->b_flags & _XBF_KMEM)
> kfree(bp->b_addr);
> + else
> + folio_put(virt_to_folio(bp->b_addr));
>
> call_rcu(&bp->b_rcu, xfs_buf_free_callback);
> }
> @@ -264,9 +241,6 @@ xfs_buf_alloc_kmem(
> bp->b_addr = NULL;
> return -ENOMEM;
> }
> - bp->b_pages = bp->b_page_array;
> - bp->b_pages[0] = kmem_to_page(bp->b_addr);
> - bp->b_page_count = 1;
> bp->b_flags |= _XBF_KMEM;
> return 0;
> }
> @@ -287,9 +261,9 @@ xfs_buf_alloc_kmem(
> * by the rest of the code - the buffer memory spans a single contiguous memory
> * region that we don't have to map and unmap to access the data directly.
> *
> - * The third type of buffer is the multi-page buffer. These are always made
> - * up of single pages so that they can be fed to vmap_ram() to return a
> - * contiguous memory region we can access the data through.
> + * The third type of buffer is the vmalloc()d buffer. This provides the buffer
> + * with the required contiguous memory region but backed by discontiguous
> + * physical pages.
> */
> static int
> xfs_buf_alloc_backing_mem(
> @@ -299,7 +273,6 @@ xfs_buf_alloc_backing_mem(
> size_t size = BBTOB(bp->b_length);
> gfp_t gfp_mask = GFP_KERNEL | __GFP_NOLOCKDEP | __GFP_NOWARN;
> struct folio *folio;
> - long filled = 0;
>
> if (xfs_buftarg_is_mem(bp->b_target))
> return xmbuf_map_page(bp);
> @@ -347,98 +320,18 @@ xfs_buf_alloc_backing_mem(
> goto fallback;
> }
> bp->b_addr = folio_address(folio);
> - bp->b_page_array[0] = &folio->page;
> - bp->b_pages = bp->b_page_array;
> - bp->b_page_count = 1;
> - bp->b_flags |= _XBF_PAGES;
> return 0;
>
> fallback:
> - /* Fall back to allocating an array of single page folios. */
> - bp->b_page_count = DIV_ROUND_UP(size, PAGE_SIZE);
> - if (bp->b_page_count <= XB_PAGES) {
> - bp->b_pages = bp->b_page_array;
> - } else {
> - bp->b_pages = kzalloc(sizeof(struct page *) * bp->b_page_count,
> - gfp_mask);
> - if (!bp->b_pages)
> - return -ENOMEM;
> - }
> - bp->b_flags |= _XBF_PAGES;
> -
> - /*
> - * Bulk filling of pages can take multiple calls. Not filling the entire
> - * array is not an allocation failure, so don't back off if we get at
> - * least one extra page.
> - */
> for (;;) {
> - long last = filled;
> -
> - filled = alloc_pages_bulk(gfp_mask, bp->b_page_count,
> - bp->b_pages);
> - if (filled == bp->b_page_count) {
> - XFS_STATS_INC(bp->b_mount, xb_page_found);
> + bp->b_addr = __vmalloc(size, gfp_mask);
> + if (bp->b_addr)
> break;
> - }
> -
> - if (filled != last)
> - continue;
> -
> - if (flags & XBF_READ_AHEAD) {
> - xfs_buf_free_pages(bp);
> + if (flags & XBF_READ_AHEAD)
> return -ENOMEM;
> - }
> -
> XFS_STATS_INC(bp->b_mount, xb_page_retries);
> memalloc_retry_wait(gfp_mask);
> }
> - return 0;
> -}
> -
> -/*
> - * Map buffer into kernel address-space if necessary.
> - */
> -STATIC int
> -_xfs_buf_map_pages(
> - struct xfs_buf *bp,
> - xfs_buf_flags_t flags)
> -{
> - ASSERT(bp->b_flags & _XBF_PAGES);
> - if (bp->b_page_count == 1) {
> - /* A single page buffer is always mappable */
> - bp->b_addr = page_address(bp->b_pages[0]);
> - } else {
> - int retried = 0;
> - unsigned nofs_flag;
> -
> - /*
> - * vm_map_ram() will allocate auxiliary structures (e.g.
> - * pagetables) with GFP_KERNEL, yet we often under a scoped nofs
> - * context here. Mixing GFP_KERNEL with GFP_NOFS allocations
> - * from the same call site that can be run from both above and
> - * below memory reclaim causes lockdep false positives. Hence we
> - * always need to force this allocation to nofs context because
> - * we can't pass __GFP_NOLOCKDEP down to auxillary structures to
> - * prevent false positive lockdep reports.
> - *
> - * XXX(dgc): I think dquot reclaim is the only place we can get
> - * to this function from memory reclaim context now. If we fix
> - * that like we've fixed inode reclaim to avoid writeback from
> - * reclaim, this nofs wrapping can go away.
> - */
> - nofs_flag = memalloc_nofs_save();
> - do {
> - bp->b_addr = vm_map_ram(bp->b_pages, bp->b_page_count,
> - -1);
> - if (bp->b_addr)
> - break;
> - vm_unmap_aliases();
> - } while (retried++ <= 1);
> - memalloc_nofs_restore(nofs_flag);
> -
> - if (!bp->b_addr)
> - return -ENOMEM;
> - }
>
> return 0;
> }
> @@ -558,7 +451,7 @@ xfs_buf_find_lock(
> return -ENOENT;
> }
> ASSERT((bp->b_flags & _XBF_DELWRI_Q) == 0);
> - bp->b_flags &= _XBF_KMEM | _XBF_PAGES;
> + bp->b_flags &= _XBF_KMEM;
> bp->b_ops = NULL;
> }
> return 0;
> @@ -744,18 +637,6 @@ xfs_buf_get_map(
> xfs_perag_put(pag);
> }
>
> - /* We do not hold a perag reference anymore. */
> - if (!bp->b_addr) {
> - error = _xfs_buf_map_pages(bp, flags);
> - if (unlikely(error)) {
> - xfs_warn_ratelimited(btp->bt_mount,
> - "%s: failed to map %u pages", __func__,
> - bp->b_page_count);
> - xfs_buf_relse(bp);
> - return error;
> - }
> - }
> -
> /*
> * Clear b_error if this is a lookup from a caller that doesn't expect
> * valid data to be found in the buffer.
> @@ -998,14 +879,6 @@ xfs_buf_get_uncached(
> if (error)
> goto fail_free_buf;
>
> - if (!bp->b_addr)
> - error = _xfs_buf_map_pages(bp, 0);
> - if (unlikely(error)) {
> - xfs_warn(target->bt_mount,
> - "%s: failed to map pages", __func__);
> - goto fail_free_buf;
> - }
> -
> trace_xfs_buf_get_uncached(bp, _RET_IP_);
> *bpp = bp;
> return 0;
> @@ -1339,7 +1212,7 @@ __xfs_buf_ioend(
> if (bp->b_flags & XBF_READ) {
> if (!bp->b_error && is_vmalloc_addr(bp->b_addr))
> invalidate_kernel_vmap_range(bp->b_addr,
> - xfs_buf_vmap_len(bp));
> + roundup(BBTOB(bp->b_length), PAGE_SIZE));
> if (!bp->b_error && bp->b_ops)
> bp->b_ops->verify_read(bp);
> if (!bp->b_error)
> @@ -1500,29 +1373,43 @@ static void
> xfs_buf_submit_bio(
> struct xfs_buf *bp)
> {
> - unsigned int size = BBTOB(bp->b_length);
> - unsigned int map = 0, p;
> + unsigned int map = 0;
> struct blk_plug plug;
> struct bio *bio;
>
> - bio = bio_alloc(bp->b_target->bt_bdev, bp->b_page_count,
> - xfs_buf_bio_op(bp), GFP_NOIO);
> - bio->bi_private = bp;
> - bio->bi_end_io = xfs_buf_bio_end_io;
> + if (is_vmalloc_addr(bp->b_addr)) {
> + unsigned int size = BBTOB(bp->b_length);
> + unsigned int alloc_size = roundup(size, PAGE_SIZE);
> + void *data = bp->b_addr;
>
> - if (bp->b_page_count == 1) {
> - __bio_add_page(bio, virt_to_page(bp->b_addr), size,
> - offset_in_page(bp->b_addr));
> - } else {
> - for (p = 0; p < bp->b_page_count; p++)
> - __bio_add_page(bio, bp->b_pages[p], PAGE_SIZE, 0);
> - bio->bi_iter.bi_size = size; /* limit to the actual size used */
> + bio = bio_alloc(bp->b_target->bt_bdev, alloc_size >> PAGE_SHIFT,
> + xfs_buf_bio_op(bp), GFP_NOIO);
> +
> + do {
> + unsigned int len = min(size, PAGE_SIZE);
>
> - if (is_vmalloc_addr(bp->b_addr))
> - flush_kernel_vmap_range(bp->b_addr,
> - xfs_buf_vmap_len(bp));
> + ASSERT(offset_in_page(data) == 0);
> + __bio_add_page(bio, vmalloc_to_page(data), len, 0);
> + data += len;
> + size -= len;
> + } while (size);
> +
> + flush_kernel_vmap_range(bp->b_addr, alloc_size);
> + } else {
> + /*
> + * Single folio or slab allocation. Must be contiguous and thus
> + * only a single bvec is needed.
> + */
> + bio = bio_alloc(bp->b_target->bt_bdev, 1, xfs_buf_bio_op(bp),
> + GFP_NOIO);
> + __bio_add_page(bio, virt_to_page(bp->b_addr),
> + BBTOB(bp->b_length),
> + offset_in_page(bp->b_addr));
> }
>
> + bio->bi_private = bp;
> + bio->bi_end_io = xfs_buf_bio_end_io;
> +
> /*
> * If there is more than one map segment, split out a new bio for each
> * map except of the last one. The last map is handled by the
> diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
> index 8db522f19b0c..db43bdc17f55 100644
> --- a/fs/xfs/xfs_buf.h
> +++ b/fs/xfs/xfs_buf.h
> @@ -36,7 +36,6 @@ struct xfs_buf;
> #define _XBF_LOGRECOVERY (1u << 18)/* log recovery buffer */
>
> /* flags used only internally */
> -#define _XBF_PAGES (1u << 20)/* backed by refcounted pages */
> #define _XBF_KMEM (1u << 21)/* backed by heap memory */
> #define _XBF_DELWRI_Q (1u << 22)/* buffer on a delwri queue */
>
> @@ -61,7 +60,6 @@ typedef unsigned int xfs_buf_flags_t;
> { XBF_STALE, "STALE" }, \
> { XBF_WRITE_FAIL, "WRITE_FAIL" }, \
> { _XBF_LOGRECOVERY, "LOG_RECOVERY" }, \
> - { _XBF_PAGES, "PAGES" }, \
> { _XBF_KMEM, "KMEM" }, \
> { _XBF_DELWRI_Q, "DELWRI_Q" }, \
> /* The following interface flags should never be set */ \
> @@ -122,8 +120,6 @@ struct xfs_buftarg {
> struct xfs_buf_cache bt_cache[];
> };
>
> -#define XB_PAGES 2
> -
> struct xfs_buf_map {
> xfs_daddr_t bm_bn; /* block number for I/O */
> int bm_len; /* size of I/O */
> @@ -185,13 +181,10 @@ struct xfs_buf {
> struct xfs_buf_log_item *b_log_item;
> struct list_head b_li_list; /* Log items list head */
> struct xfs_trans *b_transp;
> - struct page **b_pages; /* array of page pointers */
> - struct page *b_page_array[XB_PAGES]; /* inline pages */
> struct xfs_buf_map *b_maps; /* compound buffer map */
> struct xfs_buf_map __b_map; /* inline compound buffer map */
> int b_map_count;
> atomic_t b_pin_count; /* pin count */
> - unsigned int b_page_count; /* size of page array */
> int b_error; /* error code on I/O */
> void (*b_iodone)(struct xfs_buf *bp);
>
> diff --git a/fs/xfs/xfs_buf_mem.c b/fs/xfs/xfs_buf_mem.c
> index 5b64a2b3b113..b207754d2ee0 100644
> --- a/fs/xfs/xfs_buf_mem.c
> +++ b/fs/xfs/xfs_buf_mem.c
> @@ -169,9 +169,6 @@ xmbuf_map_page(
> unlock_page(page);
>
> bp->b_addr = page_address(page);
> - bp->b_pages = bp->b_page_array;
> - bp->b_pages[0] = page;
> - bp->b_page_count = 1;
> return 0;
> }
>
> @@ -180,16 +177,10 @@ void
> xmbuf_unmap_page(
> struct xfs_buf *bp)
> {
> - struct page *page = bp->b_pages[0];
> -
> ASSERT(xfs_buftarg_is_mem(bp->b_target));
>
> - put_page(page);
> -
> + put_page(virt_to_page(bp->b_addr));
> bp->b_addr = NULL;
> - bp->b_pages[0] = NULL;
> - bp->b_pages = NULL;
> - bp->b_page_count = 0;
> }
>
> /* Is this a valid daddr within the buftarg? */
> --
> 2.45.2
>
>
