Re: [PATCH] hfsplus: Convert kmap() to kmap_local_page() in bitmap.c

Viacheslav Dubeyko
2022-07-25T17:17:26Z

> On Jul 24, 2022, at 1:50 PM, Fabio M. De Francesco <fmdefrancesco@gmail.com> wrote:
>
> kmap() is being deprecated in favor of kmap_local_page().
>
> There are 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 are still valid.
>
> Since its use in bitmap.c is safe everywhere, it should be preferred.
>
> Therefore, replace kmap() with kmap_local_page() in bnode.c.
>

Looks good. Maybe, it makes sense to combine all kmap() related modifications in HFS+ into
one patchset?

Reviewed by: Viacheslav Dubeyko <slava@dubeyko.com>

Thanks,
Slava.

> Suggested-by: Ira Weiny <ira.weiny@intel.com>
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
> ---
> fs/hfsplus/bitmap.c | 18 +++++++++---------
> 1 file changed, 9 insertions(+), 9 deletions(-)
>
> diff --git a/fs/hfsplus/bitmap.c b/fs/hfsplus/bitmap.c
> index cebce0cfe340..0848b053b365 100644
> --- a/fs/hfsplus/bitmap.c
> +++ b/fs/hfsplus/bitmap.c
> @@ -39,7 +39,7 @@ int hfsplus_block_allocate(struct super_block *sb, u32 size,
> start = size;
> goto out;
> }
> - pptr = kmap(page);
> + pptr = kmap_local_page(page);
> curr = pptr + (offset & (PAGE_CACHE_BITS - 1)) / 32;
> i = offset % 32;
> offset &= ~(PAGE_CACHE_BITS - 1);
> @@ -74,7 +74,7 @@ int hfsplus_block_allocate(struct super_block *sb, u32 size,
> }
> curr++;
> }
> - kunmap(page);
> + kunmap_local(pptr);
> offset += PAGE_CACHE_BITS;
> if (offset >= size)
> break;
> @@ -127,7 +127,7 @@ int hfsplus_block_allocate(struct super_block *sb, u32 size,
> len -= 32;
> }
> set_page_dirty(page);
> - kunmap(page);
> + kunmap_local(pptr);
> offset += PAGE_CACHE_BITS;
> page = read_mapping_page(mapping, offset / PAGE_CACHE_BITS,
> NULL);
> @@ -135,7 +135,7 @@ int hfsplus_block_allocate(struct super_block *sb, u32 size,
> start = size;
> goto out;
> }
> - pptr = kmap(page);
> + pptr = kmap_local_page(page);
> curr = pptr;
> end = pptr + PAGE_CACHE_BITS / 32;
> }
> @@ -151,7 +151,7 @@ int hfsplus_block_allocate(struct super_block *sb, u32 size,
> done:
> *curr = cpu_to_be32(n);
> set_page_dirty(page);
> - kunmap(page);
> + kunmap_local(pptr);
> *max = offset + (curr - pptr) * 32 + i - start;
> sbi->free_blocks -= *max;
> hfsplus_mark_mdb_dirty(sb);
> @@ -185,7 +185,7 @@ int hfsplus_block_free(struct super_block *sb, u32 offset, u32 count)
> page = read_mapping_page(mapping, pnr, NULL);
> if (IS_ERR(page))
> goto kaboom;
> - pptr = kmap(page);
> + pptr = kmap_local_page(page);
> curr = pptr + (offset & (PAGE_CACHE_BITS - 1)) / 32;
> end = pptr + PAGE_CACHE_BITS / 32;
> len = count;
> @@ -215,11 +215,11 @@ int hfsplus_block_free(struct super_block *sb, u32 offset, u32 count)
> if (!count)
> break;
> set_page_dirty(page);
> - kunmap(page);
> + kunmap_local(pptr);
> page = read_mapping_page(mapping, ++pnr, NULL);
> if (IS_ERR(page))
> goto kaboom;
> - pptr = kmap(page);
> + pptr = kmap_local_page(page);
> curr = pptr;
> end = pptr + PAGE_CACHE_BITS / 32;
> }
> @@ -231,7 +231,7 @@ int hfsplus_block_free(struct super_block *sb, u32 offset, u32 count)
> }
> out:
> set_page_dirty(page);
> - kunmap(page);
> + kunmap_local(pptr);
> sbi->free_blocks += len;
> hfsplus_mark_mdb_dirty(sb);
> mutex_unlock(&sbi->alloc_mutex);
> --
> 2.37.1
>