From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: [PATCH] low-latency zap_page_range From: Robert Love In-Reply-To: References: Content-Type: text/plain Content-Transfer-Encoding: 7bit Date: 22 Jul 2002 11:28:21 -0700 Message-Id: <1027362501.932.56.camel@sinai> Mime-Version: 1.0 Sender: owner-linux-mm@kvack.org Return-Path: To: Linus Torvalds Cc: Andrew Morton , riel@conectiva.com.br, linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: On Mon, 2002-07-22 at 11:05, Linus Torvalds wrote: > On 22 Jul 2002, Robert Love wrote: > > > > Sure. What do you think of this? > > How about adding an "cond_resched_lock()" primitive? And this patch is an updated zap_page_range() now using the new approach I posted and Linus's suggested cond_resched_lock method (previous patch). Personally I still prefer the simpler loop method... note that the cond_resched_lock() assumes that the lock depth is ALWAYS 1 - e.g., we explicitly call schedule. A safer alternative would be break_spin_lock which will preemptively reschedule automatically, but only if preempt_count==0 (and only with the preemptible kernel enabled). This patch also has the other cleanups/optimizations from the original zap_page_range patch - same patch as before but with the new method. Patch is against 2.5 BK. Robert Love diff -urN linux-2.5.27/mm/memory.c linux/mm/memory.c --- linux-2.5.27/mm/memory.c Sat Jul 20 12:11:17 2002 +++ linux/mm/memory.c Mon Jul 22 11:18:10 2002 @@ -390,8 +390,8 @@ { pgd_t * dir; - if (address >= end) - BUG(); + BUG_ON(address >= end); + dir = pgd_offset(vma->vm_mm, address); tlb_start_vma(tlb, vma); do { @@ -402,33 +402,43 @@ tlb_end_vma(tlb, vma); } -/* - * remove user pages in a given range. +#define ZAP_BLOCK_SIZE (256 * PAGE_SIZE) /* how big a chunk we loop over */ + +/** + * zap_page_range - remove user pages in a given range + * @vma: vm_area_struct holding the applicable pages + * @address: starting address of pages to zap + * @size: number of bytes to zap */ void zap_page_range(struct vm_area_struct *vma, unsigned long address, unsigned long size) { struct mm_struct *mm = vma->vm_mm; mmu_gather_t *tlb; - pgd_t * dir; - unsigned long start = address, end = address + size; + unsigned long end, block; - dir = pgd_offset(mm, address); + spin_lock(&mm->page_table_lock); /* - * This is a long-lived spinlock. That's fine. - * There's no contention, because the page table - * lock only protects against kswapd anyway, and - * even if kswapd happened to be looking at this - * process we _want_ it to get stuck. + * This was once a long-held spinlock. Now we break the + * work up into ZAP_BLOCK_SIZE units and relinquish the + * lock after each interation. This drastically lowers + * lock contention and allows for a preemption point. */ - if (address >= end) - BUG(); - spin_lock(&mm->page_table_lock); - flush_cache_range(vma, address, end); + while (size) { + block = (size > ZAP_BLOCK_SIZE) ? ZAP_BLOCK_SIZE : size; + end = address + block; + + flush_cache_range(vma, address, end); + tlb = tlb_gather_mmu(mm, 0); + unmap_page_range(tlb, vma, address, end); + tlb_finish_mmu(tlb, address, end); + + cond_resched_lock(&mm->page_table_lock); + + address += block; + size -= block; + } - tlb = tlb_gather_mmu(mm, 0); - unmap_page_range(tlb, vma, address, end); - tlb_finish_mmu(tlb, start, end); spin_unlock(&mm->page_table_lock); } -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/