* [PATCH 1/2] mm: add cond_resched to generic_swapfile_activate
2016-07-22 21:10 [PATCH 0/2] mm patches Mikulas Patocka
@ 2016-07-22 21:11 ` Mikulas Patocka
2016-07-25 7:26 ` Michal Hocko
2016-07-22 21:12 ` [PATCH 2/2] mm: optimize copy_page_to/from_iter_iovec Mikulas Patocka
1 sibling, 1 reply; 5+ messages in thread
From: Mikulas Patocka @ 2016-07-22 21:11 UTC (permalink / raw)
To: Michal Hocko, Andrew Morton, Alexander Viro, Mel Gorman, Johannes Weiner
Cc: linux-mm, linux-kernel
The function generic_swapfile_activate can take quite long time, it iterates
over all blocks of a file, so add cond_resched to it. I observed about 1 second
stalls when activating a swapfile that was almost unfragmented - this patch
fixes it.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
---
mm/page_io.c | 2 ++
1 file changed, 2 insertions(+)
Index: linux-4.7-rc7/mm/page_io.c
===================================================================
--- linux-4.7-rc7.orig/mm/page_io.c 2016-05-30 17:34:37.000000000 +0200
+++ linux-4.7-rc7/mm/page_io.c 2016-07-11 17:23:33.000000000 +0200
@@ -166,6 +166,8 @@ int generic_swapfile_activate(struct swa
unsigned block_in_page;
sector_t first_block;
+ cond_resched();
+
first_block = bmap(inode, probe_block);
if (first_block == 0)
goto bad_bmap;
--
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* [PATCH 2/2] mm: optimize copy_page_to/from_iter_iovec
2016-07-22 21:10 [PATCH 0/2] mm patches Mikulas Patocka
2016-07-22 21:11 ` [PATCH 1/2] mm: add cond_resched to generic_swapfile_activate Mikulas Patocka
@ 2016-07-22 21:12 ` Mikulas Patocka
2016-07-23 20:59 ` Andi Kleen
1 sibling, 1 reply; 5+ messages in thread
From: Mikulas Patocka @ 2016-07-22 21:12 UTC (permalink / raw)
To: Michal Hocko, Andrew Morton, Alexander Viro, Mel Gorman, Johannes Weiner
Cc: linux-mm, linux-kernel
The functions 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
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
---
lib/iov_iter.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
Index: linux-4.7-rc7/lib/iov_iter.c
===================================================================
--- linux-4.7-rc7.orig/lib/iov_iter.c 2016-05-30 17:34:37.000000000 +0200
+++ linux-4.7-rc7/lib/iov_iter.c 2016-07-11 17:14:03.000000000 +0200
@@ -159,6 +159,7 @@ static size_t copy_page_to_iter_iovec(st
buf = iov->iov_base + skip;
copy = min(bytes, iov->iov_len - skip);
+#ifdef CONFIG_HIGHMEM
if (!fault_in_pages_writeable(buf, copy)) {
kaddr = kmap_atomic(page);
from = kaddr + offset;
@@ -190,6 +191,8 @@ static size_t copy_page_to_iter_iovec(st
copy = min(bytes, iov->iov_len - skip);
}
/* Too bad - revert to non-atomic kmap */
+#endif
+
kaddr = kmap(page);
from = kaddr + offset;
left = __copy_to_user(buf, from, copy);
@@ -208,7 +211,10 @@ static size_t copy_page_to_iter_iovec(st
bytes -= copy;
}
kunmap(page);
+
+#ifdef CONFIG_HIGHMEM
done:
+#endif
if (skip == iov->iov_len) {
iov++;
skip = 0;
@@ -240,6 +246,7 @@ static size_t copy_page_from_iter_iovec(
buf = iov->iov_base + skip;
copy = min(bytes, iov->iov_len - skip);
+#ifdef CONFIG_HIGHMEM
if (!fault_in_pages_readable(buf, copy)) {
kaddr = kmap_atomic(page);
to = kaddr + offset;
@@ -271,6 +278,8 @@ static size_t copy_page_from_iter_iovec(
copy = min(bytes, iov->iov_len - skip);
}
/* Too bad - revert to non-atomic kmap */
+#endif
+
kaddr = kmap(page);
to = kaddr + offset;
left = __copy_from_user(to, buf, copy);
@@ -289,7 +298,10 @@ static size_t copy_page_from_iter_iovec(
bytes -= copy;
}
kunmap(page);
+
+#ifdef CONFIG_HIGHMEM
done:
+#endif
if (skip == iov->iov_len) {
iov++;
skip = 0;
--
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