Here is a patch for 2.3.28 to enforce the
/proc/sys/vm/pagecache.max-percent(third argument).
It help prevent the system from pausing while large files are being read
or written.
Larry Woodman
http://www.missioncriticallinux.com
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diff --recursive linux.van/include/linux/mm.h linux.pc/include/linux/mm.h
16a17
> extern atomic_t swap_cache_pages;
443a445,450
> #define pagecache_over_max() (((unsigned long)atomic_read(&page_cache_size) - \
> atomic_read(&swap_cache_pages)) <= \
> ((page_cache.max_percent)*num_physpages/100)) ? \
> 0 : ((atomic_read(&page_cache_size) - \
> atomic_read(&swap_cache_pages))- \
> (page_cache.max_percent*num_physpages/100))
diff --recursive linux.van/include/linux/pagemap.h linux.pc/include/linux/pagemap.h
30c30
< #define page_cache_alloc() alloc_pages(GFP_HIGHUSER, 0)
---
> extern struct page * page_cache_alloc(void);
diff --recursive linux.van/mm/filemap.c linux.pc/mm/filemap.c
362a363,454
> /* Try to shrink the pagecache */
> void shrink_pagecache(long over)
> {
> int count;
> LIST_HEAD(young);
> LIST_HEAD(old);
> struct list_head *page_lru = 0;
> struct page * page;
>
> spin_lock(&pagemap_lru_lock);
> count = nr_lru_pages;
>
> while ((count-- > 1) && (over > 0) && (page_lru = lru_cache.prev) != &lru_cache) {
> page = list_entry(page_lru, struct page, lru);
> list_del(page_lru);
>
> /* if the page has been used just put it back on the tail */
> if (test_and_clear_bit(PG_referenced, &page->flags)) {
> list_add(page_lru, &lru_cache);
> continue;
> }
> spin_unlock(&pagemap_lru_lock);
>
> /* dont bother with dma-able or high memory pages here */
> if (PageDMA(page) || PageHighMem(page)) {
> list_add(page_lru, &old);
> spin_lock(&pagemap_lru_lock);
> continue;
> }
>
> /* skip over swapcache and currently locked pages this time */
> if (PageSwapCache(page) || TryLockPage(page)) {
> list_add(page_lru, &young);
> spin_lock(&pagemap_lru_lock);
> continue;
> }
>
> /* protect next if statement */
> spin_lock(&pagecache_lock);
> get_page(page);
>
> /* available if mapping&count==2 or mapping&buffers&count=3 */
> if (page->mapping && (page_count(page)==2 ||
> (page->buffers && page_count(page)==3))) {
> if (page->buffers) {
> spin_unlock(&pagecache_lock);
> if (!try_to_free_buffers(page)) {
> list_add(page_lru, &old);
> UnlockPage(page);
> put_page(page);
> spin_lock(&pagemap_lru_lock);
> continue;
> } else
> spin_lock(&pagecache_lock);
> }
> if (page->mapping) {
> remove_page_from_inode_queue(page);
> remove_page_from_hash_queue(page);
> page->mapping = NULL;
> spin_unlock(&pagecache_lock);
> UnlockPage(page);
> put_page(page);
> page_cache_release(page);
> over--;
> spin_lock(&pagemap_lru_lock);
> nr_lru_pages--;
> }
> } else {
> spin_unlock(&pagecache_lock);
> list_add(page_lru, &young);
> UnlockPage(page);
> put_page(page);
> spin_lock(&pagemap_lru_lock);
> }
> }
>
> /* put the young pages on the head and the old pages on the tail */
> list_splice(&young, &lru_cache);
> list_splice(&old, lru_cache.prev);
> spin_unlock(&pagemap_lru_lock);
> return;
> }
>
> struct page * page_cache_alloc(void)
> {
> unsigned long over;
>
> if ((over = pagecache_over_max()) > 0)
> shrink_pagecache(over);
> return(alloc_pages(GFP_HIGHUSER, 0));
> }
>
diff --recursive linux.van/mm/swap_state.c linux.pc/mm/swap_state.c
27a28,29
> atomic_t swap_cache_pages = ATOMIC_INIT(0);
>
52a55
> atomic_inc(&swap_cache_pages);
152a156
> atomic_dec(&swap_cache_pages);
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