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hfsplus: convert kmap() to kmap_local_page() in bitmap.c

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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 bitmap.c.

Tested in a QEMU/KVM x86_32 VM, 6GB RAM, booting a kernel with
HIGHMEM64GB enabled.

Link: https://lkml.kernel.org/r/20220809203105.26183-4-fmdefrancesco@gmail.com
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Suggested-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Viacheslav Dubeyko <slava@dubeyko.com>
Cc: Bart Van Assche <bvanassche@acm.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Kees Cook <keescook@chromium.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Fabio M. De Francesco 2022-08-09 22:31:04 +02:00 committed by Andrew Morton
parent 6c3014a67a
commit f9ef3b95a3
1 changed files with 10 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
fs/hfsplus/bitmap.c
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@ -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;
@ -84,7 +84,7 @@ int hfsplus_block_allocate(struct super_block *sb, u32 size,
start = size;
goto out;
}
curr = pptr = kmap(page);
curr = pptr = kmap_local_page(page);
if ((size ^ offset) / PAGE_CACHE_BITS)
end = pptr + PAGE_CACHE_BITS / 32;
else
@ -127,7 +127,7 @@ found:
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 @@ found:
start = size;
goto out;
}
pptr = kmap(page);
pptr = kmap_local_page(page);
curr = pptr;
end = pptr + PAGE_CACHE_BITS / 32;
}
@ -151,7 +151,7 @@ last:
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 @@ done:
}
out:
set_page_dirty(page);
kunmap(page);
kunmap_local(pptr);
sbi->free_blocks += len;
hfsplus_mark_mdb_dirty(sb);
mutex_unlock(&sbi->alloc_mutex);