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Date: Tue, 9 Aug 2022 15:17:32 -0700
From: Viacheslav Dubeyko <slava@...eyko.com>
To: "Fabio M. De Francesco" <fmdefrancesco@...il.com>
Cc: "Matthew Wilcox (Oracle)" <willy@...radead.org>,
Ira Weiny <ira.weiny@...el.com>, Jens Axboe <axboe@...nel.dk>,
Andrew Morton <akpm@...ux-foundation.org>,
Bart Van Assche <bvanassche@....org>,
Kees Cook <keescook@...omium.org>,
Muchun Song <songmuchun@...edance.com>,
Linux FS Devel <linux-fsdevel@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/4] hfsplus: Convert kmap() to kmap_local_page() in
bnode.c
> On Aug 9, 2022, at 1:31 PM, Fabio M. De Francesco <fmdefrancesco@...il.com> wrote:
>
> kmap() is being deprecated in favor of kmap_local_page().
>
> Two main problems with kmap(): (1) It comes with an overhead as mapping
> space is restricted and protected by a global lock for synchronization and
> (2) it also requires global TLB invalidation when the kmap’s pool wraps
> and it might block when the mapping space is fully utilized until a slot
> becomes available.
>
> With kmap_local_page() the mappings are per thread, CPU local, can take
> page faults, and can be called from any context (including interrupts).
> It is faster than kmap() in kernels with HIGHMEM enabled. Furthermore,
> the tasks can be preempted and, when they are scheduled to run again, the
> kernel virtual addresses are restored and still valid.
>
> Since its use in bnode.c is safe everywhere, it should be preferred.
>
> Therefore, replace kmap() with kmap_local_page() in bnode.c. Where
> possible, use the suited standard helpers (memzero_page(), memcpy_page())
> instead of open coding kmap_local_page() plus memset() or memcpy().
>
> Tested in a QEMU/KVM x86_32 VM, 6GB RAM, booting a kernel with
> HIGHMEM64GB enabled.
>
> Cc: Viacheslav Dubeyko <slava@...eyko.com>
> Suggested-by: Ira Weiny <ira.weiny@...el.com>
> Reviewed-by: Ira Weiny <ira.weiny@...el.com>
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
> ---
Looks good.
Reviewed-by: Viacheslav Dubeyko <slava@...eyko.com>
Thanks,
Slava.
> fs/hfsplus/bnode.c | 105 +++++++++++++++++++++------------------------
> 1 file changed, 48 insertions(+), 57 deletions(-)
>
> diff --git a/fs/hfsplus/bnode.c b/fs/hfsplus/bnode.c
> index a5ab00e54220..87974d5e6791 100644
> --- a/fs/hfsplus/bnode.c
> +++ b/fs/hfsplus/bnode.c
> @@ -29,14 +29,12 @@ void hfs_bnode_read(struct hfs_bnode *node, void *buf, int off, int len)
> off &= ~PAGE_MASK;
>
> l = min_t(int, len, PAGE_SIZE - off);
> - memcpy(buf, kmap(*pagep) + off, l);
> - kunmap(*pagep);
> + memcpy_from_page(buf, *pagep, off, l);
>
> while ((len -= l) != 0) {
> buf += l;
> l = min_t(int, len, PAGE_SIZE);
> - memcpy(buf, kmap(*++pagep), l);
> - kunmap(*pagep);
> + memcpy_from_page(buf, *++pagep, 0, l);
> }
> }
>
> @@ -82,16 +80,14 @@ void hfs_bnode_write(struct hfs_bnode *node, void *buf, int off, int len)
> off &= ~PAGE_MASK;
>
> l = min_t(int, len, PAGE_SIZE - off);
> - memcpy(kmap(*pagep) + off, buf, l);
> + memcpy_to_page(*pagep, off, buf, l);
> set_page_dirty(*pagep);
> - kunmap(*pagep);
>
> while ((len -= l) != 0) {
> buf += l;
> l = min_t(int, len, PAGE_SIZE);
> - memcpy(kmap(*++pagep), buf, l);
> + memcpy_to_page(*++pagep, 0, buf, l);
> set_page_dirty(*pagep);
> - kunmap(*pagep);
> }
> }
>
> @@ -112,15 +108,13 @@ void hfs_bnode_clear(struct hfs_bnode *node, int off, int len)
> off &= ~PAGE_MASK;
>
> l = min_t(int, len, PAGE_SIZE - off);
> - memset(kmap(*pagep) + off, 0, l);
> + memzero_page(*pagep, off, l);
> set_page_dirty(*pagep);
> - kunmap(*pagep);
>
> while ((len -= l) != 0) {
> l = min_t(int, len, PAGE_SIZE);
> - memset(kmap(*++pagep), 0, l);
> + memzero_page(*++pagep, 0, l);
> set_page_dirty(*pagep);
> - kunmap(*pagep);
> }
> }
>
> @@ -142,24 +136,20 @@ void hfs_bnode_copy(struct hfs_bnode *dst_node, int dst,
>
> if (src == dst) {
> l = min_t(int, len, PAGE_SIZE - src);
> - memcpy(kmap(*dst_page) + src, kmap(*src_page) + src, l);
> - kunmap(*src_page);
> + memcpy_page(*dst_page, src, *src_page, src, l);
> set_page_dirty(*dst_page);
> - kunmap(*dst_page);
>
> while ((len -= l) != 0) {
> l = min_t(int, len, PAGE_SIZE);
> - memcpy(kmap(*++dst_page), kmap(*++src_page), l);
> - kunmap(*src_page);
> + memcpy_page(*++dst_page, 0, *++src_page, 0, l);
> set_page_dirty(*dst_page);
> - kunmap(*dst_page);
> }
> } else {
> void *src_ptr, *dst_ptr;
>
> do {
> - src_ptr = kmap(*src_page) + src;
> - dst_ptr = kmap(*dst_page) + dst;
> + dst_ptr = kmap_local_page(*dst_page) + dst;
> + src_ptr = kmap_local_page(*src_page) + src;
> if (PAGE_SIZE - src < PAGE_SIZE - dst) {
> l = PAGE_SIZE - src;
> src = 0;
> @@ -171,9 +161,9 @@ void hfs_bnode_copy(struct hfs_bnode *dst_node, int dst,
> }
> l = min(len, l);
> memcpy(dst_ptr, src_ptr, l);
> - kunmap(*src_page);
> + kunmap_local(src_ptr);
> set_page_dirty(*dst_page);
> - kunmap(*dst_page);
> + kunmap_local(dst_ptr);
> if (!dst)
> dst_page++;
> else
> @@ -185,6 +175,7 @@ void hfs_bnode_copy(struct hfs_bnode *dst_node, int dst,
> void hfs_bnode_move(struct hfs_bnode *node, int dst, int src, int len)
> {
> struct page **src_page, **dst_page;
> + void *src_ptr, *dst_ptr;
> int l;
>
> hfs_dbg(BNODE_MOD, "movebytes: %u,%u,%u\n", dst, src, len);
> @@ -202,27 +193,28 @@ void hfs_bnode_move(struct hfs_bnode *node, int dst, int src, int len)
>
> if (src == dst) {
> while (src < len) {
> - memmove(kmap(*dst_page), kmap(*src_page), src);
> - kunmap(*src_page);
> + dst_ptr = kmap_local_page(*dst_page);
> + src_ptr = kmap_local_page(*src_page);
> + memmove(dst_ptr, src_ptr, src);
> + kunmap_local(src_ptr);
> set_page_dirty(*dst_page);
> - kunmap(*dst_page);
> + kunmap_local(dst_ptr);
> len -= src;
> src = PAGE_SIZE;
> src_page--;
> dst_page--;
> }
> src -= len;
> - memmove(kmap(*dst_page) + src,
> - kmap(*src_page) + src, len);
> - kunmap(*src_page);
> + dst_ptr = kmap_local_page(*dst_page);
> + src_ptr = kmap_local_page(*src_page);
> + memmove(dst_ptr + src, src_ptr + src, len);
> + kunmap_local(src_ptr);
> set_page_dirty(*dst_page);
> - kunmap(*dst_page);
> + kunmap_local(dst_ptr);
> } else {
> - void *src_ptr, *dst_ptr;
> -
> do {
> - src_ptr = kmap(*src_page) + src;
> - dst_ptr = kmap(*dst_page) + dst;
> + dst_ptr = kmap_local_page(*dst_page) + dst;
> + src_ptr = kmap_local_page(*src_page) + src;
> if (src < dst) {
> l = src;
> src = PAGE_SIZE;
> @@ -234,9 +226,9 @@ void hfs_bnode_move(struct hfs_bnode *node, int dst, int src, int len)
> }
> l = min(len, l);
> memmove(dst_ptr - l, src_ptr - l, l);
> - kunmap(*src_page);
> + kunmap_local(src_ptr);
> set_page_dirty(*dst_page);
> - kunmap(*dst_page);
> + kunmap_local(dst_ptr);
> if (dst == PAGE_SIZE)
> dst_page--;
> else
> @@ -251,26 +243,27 @@ void hfs_bnode_move(struct hfs_bnode *node, int dst, int src, int len)
>
> if (src == dst) {
> l = min_t(int, len, PAGE_SIZE - src);
> - memmove(kmap(*dst_page) + src,
> - kmap(*src_page) + src, l);
> - kunmap(*src_page);
> +
> + dst_ptr = kmap_local_page(*dst_page) + src;
> + src_ptr = kmap_local_page(*src_page) + src;
> + memmove(dst_ptr, src_ptr, l);
> + kunmap_local(src_ptr);
> set_page_dirty(*dst_page);
> - kunmap(*dst_page);
> + kunmap_local(dst_ptr);
>
> while ((len -= l) != 0) {
> l = min_t(int, len, PAGE_SIZE);
> - memmove(kmap(*++dst_page),
> - kmap(*++src_page), l);
> - kunmap(*src_page);
> + dst_ptr = kmap_local_page(*++dst_page);
> + src_ptr = kmap_local_page(*++src_page);
> + memmove(dst_ptr, src_ptr, l);
> + kunmap_local(src_ptr);
> set_page_dirty(*dst_page);
> - kunmap(*dst_page);
> + kunmap_local(dst_ptr);
> }
> } else {
> - void *src_ptr, *dst_ptr;
> -
> do {
> - src_ptr = kmap(*src_page) + src;
> - dst_ptr = kmap(*dst_page) + dst;
> + dst_ptr = kmap_local_page(*dst_page) + dst;
> + src_ptr = kmap_local_page(*src_page) + src;
> if (PAGE_SIZE - src <
> PAGE_SIZE - dst) {
> l = PAGE_SIZE - src;
> @@ -283,9 +276,9 @@ void hfs_bnode_move(struct hfs_bnode *node, int dst, int src, int len)
> }
> l = min(len, l);
> memmove(dst_ptr, src_ptr, l);
> - kunmap(*src_page);
> + kunmap_local(src_ptr);
> set_page_dirty(*dst_page);
> - kunmap(*dst_page);
> + kunmap_local(dst_ptr);
> if (!dst)
> dst_page++;
> else
> @@ -498,14 +491,14 @@ struct hfs_bnode *hfs_bnode_find(struct hfs_btree *tree, u32 num)
> if (!test_bit(HFS_BNODE_NEW, &node->flags))
> return node;
>
> - desc = (struct hfs_bnode_desc *)(kmap(node->page[0]) +
> - node->page_offset);
> + desc = (struct hfs_bnode_desc *)(kmap_local_page(node->page[0]) +
> + node->page_offset);
> node->prev = be32_to_cpu(desc->prev);
> node->next = be32_to_cpu(desc->next);
> node->num_recs = be16_to_cpu(desc->num_recs);
> node->type = desc->type;
> node->height = desc->height;
> - kunmap(node->page[0]);
> + kunmap_local(desc);
>
> switch (node->type) {
> case HFS_NODE_HEADER:
> @@ -589,14 +582,12 @@ struct hfs_bnode *hfs_bnode_create(struct hfs_btree *tree, u32 num)
> }
>
> pagep = node->page;
> - memset(kmap(*pagep) + node->page_offset, 0,
> - min_t(int, PAGE_SIZE, tree->node_size));
> + memzero_page(*pagep, node->page_offset,
> + min_t(int, PAGE_SIZE, tree->node_size));
> set_page_dirty(*pagep);
> - kunmap(*pagep);
> for (i = 1; i < tree->pages_per_bnode; i++) {
> - memset(kmap(*++pagep), 0, PAGE_SIZE);
> + memzero_page(*++pagep, 0, PAGE_SIZE);
> set_page_dirty(*pagep);
> - kunmap(*pagep);
> }
> clear_bit(HFS_BNODE_NEW, &node->flags);
> wake_up(&node->lock_wq);
> --
> 2.37.1
>
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