>Continuing thinking about the code I just found a race condition between
>the page-LRU shrink_mmap and truncate_inode_pages() ;).
I did some more profiling and I noticed a performance problem.
I had to join the two global page-lru headers into one, since in the
lru-patch I am proposing for inclusion I removed the code to take the
pages mapped in process space (so unfreeable from shrink_mmap) out of the
lru list (since it was increasing a lot the complxity of the code now that
everything is SMP threaded).
So with the current code that still uses the double lru-lists but is not
capable to skip the mapped-pages, if there would be 10mbyte of swap cache
mapped in process space I would end up trying to free such 10mbyte of
memory at each shrink_mmap pass... not good. NOTE: this performance
problem can trigger only with swap cache mapped in the process space (I
couldn't notice that with the kernel compile bench).
The reason I was using two lists is that shrinking the swap cache before
touching the page-cache _far_ better preserve the working set.
So here it is a strighforward patch (incremental to the second I posted
today) to take all pages queued in the same lru list. These are only
details, the core of the code doesn't change at all:
diff -ur 2.3.12-lruswap/fs/buffer.c 2.3.12-lru/fs/buffer.c
--- 2.3.12-lruswap/fs/buffer.c Wed Aug 4 19:17:22 1999
+++ 2.3.12-lru/fs/buffer.c Wed Aug 4 19:24:08 1999
@@ -1953,7 +1953,7 @@
page_map = mem_map + MAP_NR(page);
page_map->buffers = bh;
- lru_cache_add(page_map, 0);
+ lru_cache_add(page_map);
atomic_add(PAGE_SIZE, &buffermem);
return 1;
}
diff -ur 2.3.12-lruswap/include/linux/swap.h 2.3.12-lru/include/linux/swap.h
--- 2.3.12-lruswap/include/linux/swap.h Wed Aug 4 19:17:22 1999
+++ 2.3.12-lru/include/linux/swap.h Wed Aug 4 19:15:26 1999
@@ -65,7 +65,7 @@
extern int nr_swap_pages;
extern int nr_free_pages;
extern int nr_lru_pages;
-extern struct list_head lru_cache, lru_swap_cache;
+extern struct list_head lru_cache;
extern atomic_t nr_async_pages;
extern struct inode swapper_inode;
extern atomic_t page_cache_size;
@@ -168,12 +168,12 @@
/*
* Helper macros for lru_pages handling.
*/
-#define lru_cache_add(page, swap_cache) \
-do { \
- spin_lock(&pagemap_lru_lock); \
- list_add(&(page)->lru, !(swap_cache) ? &lru_cache:&lru_swap_cache); \
- nr_lru_pages++; \
- spin_unlock(&pagemap_lru_lock); \
+#define lru_cache_add(page) \
+do { \
+ spin_lock(&pagemap_lru_lock); \
+ list_add(&(page)->lru, &lru_cache); \
+ nr_lru_pages++; \
+ spin_unlock(&pagemap_lru_lock); \
} while (0)
#define lru_cache_del(page) \
diff -ur 2.3.12-lruswap/mm/filemap.c 2.3.12-lru/mm/filemap.c
--- 2.3.12-lruswap/mm/filemap.c Wed Aug 4 19:17:23 1999
+++ 2.3.12-lru/mm/filemap.c Wed Aug 4 19:23:14 1999
@@ -223,22 +223,25 @@
extern atomic_t too_many_dirty_buffers;
-static inline int shrink_mmap_lru(struct list_head * lru, int * count,
- int gfp_mask)
+int shrink_mmap(int priority, int gfp_mask)
{
- int ret = 0;
+ int ret = 0, count;
LIST_HEAD(young);
LIST_HEAD(old);
LIST_HEAD(forget);
struct list_head * page_lru, * dispose;
struct page * page;
- while (*count > 0 && (page_lru = lru->prev) != lru)
+ count = nr_lru_pages / (priority+1);
+
+ spin_lock(&pagemap_lru_lock);
+
+ while (count > 0 && (page_lru = lru_cache.prev) != &lru_cache)
{
page = list_entry(page_lru, struct page, lru);
list_del(page_lru);
- dispose = lru;
+ dispose = &lru_cache;
if (test_and_clear_bit(PG_referenced, &page->flags))
/* Roll the page at the top of the lru list,
* we could also be more aggressive putting
@@ -252,7 +255,7 @@
if ((gfp_mask & __GFP_DMA) && !PageDMA(page))
goto dispose_continue;
- (*count)--;
+ count--;
dispose = &young;
if (TryLockPage(page))
@@ -362,23 +365,8 @@
nr_lru_pages--;
out:
- list_splice(&young, lru);
- list_splice(&old, lru->prev);
-
- return ret;
-}
-
-int shrink_mmap(int priority, int gfp_mask)
-{
- int ret = 0, count, i;
- struct list_head * lru[2] = { &lru_swap_cache, &lru_cache, };
-
- count = nr_lru_pages / (priority+1);
-
- spin_lock(&pagemap_lru_lock);
-
- for (i=0; count > 0 && !ret && i<2; i++)
- ret = shrink_mmap_lru(lru[i], &count, gfp_mask);
+ list_splice(&young, &lru_cache);
+ list_splice(&old, lru_cache.prev);
spin_unlock(&pagemap_lru_lock);
@@ -506,7 +494,7 @@
page->offset = offset;
add_page_to_inode_queue(inode, page);
__add_page_to_hash_queue(page, hash);
- lru_cache_add(page, PageSwapCache(page));
+ lru_cache_add(page);
}
void add_to_page_cache(struct page * page, struct inode * inode, unsigned long offset)
diff -ur 2.3.12-lruswap/mm/page_alloc.c 2.3.12-lru/mm/page_alloc.c
--- 2.3.12-lruswap/mm/page_alloc.c Wed Aug 4 19:17:23 1999
+++ 2.3.12-lru/mm/page_alloc.c Wed Aug 4 19:16:33 1999
@@ -22,7 +22,6 @@
int nr_free_pages = 0;
int nr_lru_pages;
LIST_HEAD(lru_cache);
-LIST_HEAD(lru_swap_cache);
/*
* Free area management
Now the profile numbers are fine. With 6mbyte of swap cache mapped in
memory I am running in background `cat /usr/bin/* /usr/X11R6/bin/*
>/dev/null` and a `cp /dev/hda /dev/null` and these are the profiling
numbers I get:
andrea@laser:~ > readprofile -m /System.map |sort -nr | head -20
12536 total 0.0193
12236 cpu_idle 145.6667
62 file_read_actor 0.8158
21 ide_set_handler 0.2917
16 startup_32 0.0976
12 try_to_free_buffers 0.0246
12 kmem_cache_free 0.0280
12 do_rw_disk 0.0175
10 ide_do_request 0.0072
8 do_generic_file_read 0.0036
7 shrink_mmap 0.0068
6 free_pages 0.0174
6 block_read_full_page 0.0118
5 schedule 0.0034
5 remove_page_from_inode_queue 0.0833
5 ide_wait_stat 0.0231
5 ide_dmaproc 0.0137
5 get_unused_buffer_head 0.0192
5 get_hash_table 0.0291
5 ext2_get_block 0.0037
As you can see try_to_free_buffers is eating far more CPU than
shrink_mmap.
I also uploaded a whole patch against clean 2.3.12 that merges all the
three patches here, if somebody would try it out please feedback ;).
ftp://e-mind.com/pub/andrea/kernel-patches/2.3.12/page_lru-2.3.12-H
ftp://ftp.suse.com/pub/people/andrea/kernel-patches/2.3.12/page_lru-2.3.12-H
Andrea
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