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authorMikulas Patocka <mpatocka@redhat.com>2016-07-28 15:48:50 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2016-07-28 16:07:41 -0700
commit3fa6c507319c897598512da91c010a4ad2ed682c (patch)
treec7746f5b4cca6489f11030db7e19f21de947ed04 /lib
parent7e4411bfe6dd29713f879717b433304a1992526d (diff)
downloadlinux-stericsson-3fa6c507319c897598512da91c010a4ad2ed682c.tar.gz
mm: optimize copy_page_to/from_iter_iovec
copy_page_to_iter_iovec() and copy_page_from_iter_iovec() copy some data to userspace or from userspace. These functions have a fast path where they map a page using kmap_atomic and a slow path where they use kmap. kmap is slower than kmap_atomic, so the fast path is preferred. However, on kernels without highmem support, kmap just calls page_address, so there is no need to avoid kmap. On kernels without highmem support, the fast path just increases code size (and cache footprint) and it doesn't improve copy performance in any way. This patch enables the fast path only if CONFIG_HIGHMEM is defined. Code size reduced by this patch: x86 (without highmem) 928 x86-64 960 sparc64 848 alpha 1136 pa-risc 1200 [akpm@linux-foundation.org: use IS_ENABLED(), per Andi] Link: http://lkml.kernel.org/r/alpine.LRH.2.02.1607221711410.4818@file01.intranet.prod.int.rdu2.redhat.com Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Mel Gorman <mgorman@suse.de> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Andi Kleen <andi@firstfloor.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'lib')
-rw-r--r--lib/iov_iter.c8
1 files changed, 6 insertions, 2 deletions
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index d67c8288d95d..9e8c7386b3a0 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -144,7 +144,7 @@ static size_t copy_page_to_iter_iovec(struct page *page, size_t offset, size_t b
buf = iov->iov_base + skip;
copy = min(bytes, iov->iov_len - skip);
- if (!fault_in_pages_writeable(buf, copy)) {
+ if (IS_ENABLED(CONFIG_HIGHMEM) && !fault_in_pages_writeable(buf, copy)) {
kaddr = kmap_atomic(page);
from = kaddr + offset;
@@ -175,6 +175,7 @@ static size_t copy_page_to_iter_iovec(struct page *page, size_t offset, size_t b
copy = min(bytes, iov->iov_len - skip);
}
/* Too bad - revert to non-atomic kmap */
+
kaddr = kmap(page);
from = kaddr + offset;
left = __copy_to_user(buf, from, copy);
@@ -193,6 +194,7 @@ static size_t copy_page_to_iter_iovec(struct page *page, size_t offset, size_t b
bytes -= copy;
}
kunmap(page);
+
done:
if (skip == iov->iov_len) {
iov++;
@@ -225,7 +227,7 @@ static size_t copy_page_from_iter_iovec(struct page *page, size_t offset, size_t
buf = iov->iov_base + skip;
copy = min(bytes, iov->iov_len - skip);
- if (!fault_in_pages_readable(buf, copy)) {
+ if (IS_ENABLED(CONFIG_HIGHMEM) && !fault_in_pages_readable(buf, copy)) {
kaddr = kmap_atomic(page);
to = kaddr + offset;
@@ -256,6 +258,7 @@ static size_t copy_page_from_iter_iovec(struct page *page, size_t offset, size_t
copy = min(bytes, iov->iov_len - skip);
}
/* Too bad - revert to non-atomic kmap */
+
kaddr = kmap(page);
to = kaddr + offset;
left = __copy_from_user(to, buf, copy);
@@ -274,6 +277,7 @@ static size_t copy_page_from_iter_iovec(struct page *page, size_t offset, size_t
bytes -= copy;
}
kunmap(page);
+
done:
if (skip == iov->iov_len) {
iov++;