Hi,
the patch below fixes the problem introduced in -ac21 (freeing
too many pages from a "wrong" zone) and at the same time should
increase interactive performance a bit.
The patch also fixes the situation where unneeded CPU time is
wasted and the potential for an infinite loop in shrink_mmap().
I've tested this patch in various circumstances with various
amounts of memory and it seems to work quite well...
The only situation where stalls still occur is when memory is
completely filled with dirty pages, but as we determined earlier
there is no good fix for this without write throttling...
regards,
Rik
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--- linux-2.4.0-t1-ac22-riel/fs/buffer.c.orig Mon Jun 19 18:24:09 2000 +++ linux-2.4.0-t1-ac22-riel/fs/buffer.c Mon Jun 19 21:37:26 2000 @@ -2387,6 +2387,11 @@ * NOTE: There are quite a number of ways that threads of control can * obtain a reference to a buffer head within a page. So we must * lock out all of these paths to cleanly toss the page. + * + * Different values for wait: + * -1: don't do IO to free the buffers associated with page + * 0: start asynchronous IO to free the buffers + * 1: wait until the buffers have been freed */ int try_to_free_buffers(struct page * page, int wait) { @@ -2441,7 +2446,7 @@ spin_unlock(&free_list[index].lock); write_unlock(&hash_table_lock); spin_unlock(&lru_list_lock); - if (sync_page_buffers(bh, wait)) + if (wait >= 0 && sync_page_buffers(bh, wait)) goto again; return 0; } --- linux-2.4.0-t1-ac22-riel/mm/filemap.c.orig Mon Jun 19 18:27:05 2000 +++ linux-2.4.0-t1-ac22-riel/mm/filemap.c Tue Jun 20 13:19:36 2000 @@ -301,16 +301,19 @@ */ int shrink_mmap(int priority, int gfp_mask) { - int ret = 0, count, nr_dirty; + int ret = 0, count, maxscan, nr_dirty, loop = 0; struct list_head * page_lru; struct page * page = NULL; +shrink_again: count = nr_lru_pages / (priority + 1); - nr_dirty = priority; + maxscan = nr_lru_pages; + nr_dirty = 0; /* we need pagemap_lru_lock for list_del() ... subtle code below */ spin_lock(&pagemap_lru_lock); - while (count > 0 && (page_lru = lru_cache.prev) != &lru_cache) { + while ((count > 0) && (maxscan-- > 0) && + (page_lru = lru_cache.prev) != &lru_cache) { page = list_entry(page_lru, struct page, lru); list_del(page_lru); @@ -351,9 +354,12 @@ * of zone - it's old. */ if (page->buffers) { - int wait = ((gfp_mask & __GFP_IO) && (nr_dirty-- < 0)); + int wait = ((gfp_mask & __GFP_IO) ? 0 : -1); + nr_dirty++; if (!try_to_free_buffers(page, wait)) goto unlock_continue; + /* We freed the buffers so it wasn't dirty */ + nr_dirty--; /* page was locked, inode can't go away under us */ if (!page->mapping) { atomic_dec(&buffermem_pages); @@ -361,6 +367,15 @@ } } + /* + * Are there more than enough free pages in this zone? + * Don't drop the page since it contains useful data. + */ + if (page->zone->free_pages > page->zone->pages_high) { + count++; + goto unlock_continue; + } + /* Take the pagecache_lock spinlock held to avoid other tasks to notice the page while we are looking at its page count. If it's a pagecache-page we'll free it @@ -387,6 +402,7 @@ } /* PageDeferswap -> we swap out the page now. */ if (gfp_mask & __GFP_IO) { + nr_dirty++; spin_unlock(&pagecache_lock); /* Do NOT unlock the page ... brw_page does. */ ClearPageDirty(page); @@ -433,6 +449,17 @@ out: spin_unlock(&pagemap_lru_lock); + + /* We scheduled pages for IO? Wake up kflushd. */ + if (nr_dirty) { + if (!loop && !ret && (gfp_mask & __GFP_IO)) { + loop = 1; + wakeup_bdflush(1); + goto shrink_again; + } else { + wakeup_bdflush(0); + } + } return ret; } --- linux-2.4.0-t1-ac22-riel/mm/vmscan.c.orig Mon Jun 19 18:27:05 2000 +++ linux-2.4.0-t1-ac22-riel/mm/vmscan.c Mon Jun 19 19:02:28 2000 @@ -186,9 +186,7 @@ flush_tlb_page(vma, address); vmlist_access_unlock(vma->vm_mm); - /* OK, do a physical asynchronous write to swap. */ - // rw_swap_page(WRITE, page, 0); - /* Let shrink_mmap handle this swapout. */ + /* Mark the page for swapout. Shrink_mmap does the hard work. */ SetPageDirty(page); UnlockPage(page); @@ -427,6 +425,32 @@ return __ret; } +/** + * memory_pressure - check if the system is under memory pressure + * + * Returns 1 if the system is low on memory in at least one zone, + * 0 otherwise + */ +int memory_pressure(void) +{ + pg_data_t *pgdat = pgdat_list; + + do { + int i; + for(i = 0; i < MAX_NR_ZONES; i++) { + zone_t *zone = pgdat->node_zones + i; + if (!zone->size || !zone->zone_wake_kswapd) + continue; + if (zone->free_pages < zone->pages_low) + return 1; + } + pgdat = pgdat->node_next; + } while (pgdat); + + /* Found no zone with memory pressure? */ + return 0; +} + /* * We need to make the locks finer granularity, but right * now we need this so that we can do page allocations @@ -458,6 +482,8 @@ goto done; } + if (!memory_pressure()) + return 1; /* Try to get rid of some shared memory pages.. */ if (gfp_mask & __GFP_IO) { @@ -512,7 +538,7 @@ } else { priority--; } - } while (priority >= 0); + } while (priority >= 0 && memory_pressure()); /* Always end on a shrink_mmap.. */ while (shrink_mmap(0, gfp_mask)) { @@ -521,6 +547,9 @@ goto done; } + if (!memory_pressure()) + ret = 1; + done: return ret; } @@ -563,30 +592,22 @@ */ tsk->flags |= PF_MEMALLOC; + /* + * Kswapd needs to run for the entire lifetime of the system... + */ for (;;) { - pg_data_t *pgdat; - int something_to_do = 0; - - pgdat = pgdat_list; - do { - int i; - for(i = 0; i < MAX_NR_ZONES; i++) { - zone_t *zone = pgdat->node_zones+ i; - if (tsk->need_resched) - schedule(); - if (!zone->size || !zone->zone_wake_kswapd) - continue; - if (zone->free_pages < zone->pages_low) - something_to_do = 1; - do_try_to_free_pages(GFP_KSWAPD); - } - pgdat = pgdat->node_next; - } while (pgdat); - - if (!something_to_do) { + if (memory_pressure()) { + /* If there is memory pressure, try to free pages. */ + do_try_to_free_pages(GFP_KSWAPD); + } else { + /* Else, we sleep and wait for somebody to wake us. */ tsk->state = TASK_INTERRUPTIBLE; interruptible_sleep_on(&kswapd_wait); } + + /* Yield if something more important needs to run. */ + if (tsk->need_resched) + schedule(); } } --- linux-2.4.0-t1-ac22-riel/include/linux/swap.h.orig Mon Jun 19 19:03:56 2000 +++ linux-2.4.0-t1-ac22-riel/include/linux/swap.h Mon Jun 19 19:08:00 2000 @@ -87,6 +87,7 @@ /* linux/mm/vmscan.c */ extern int try_to_free_pages(unsigned int gfp_mask); +extern int memory_pressure(void); /* linux/mm/page_io.c */ extern void rw_swap_page(int, struct page *, int);
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This archive was generated by hypermail 2b29 : Fri Jun 23 2000 - 21:00:20 EST