Re: [PATCH 2/2] Wait for page writeback when directly reclaiming contiguous areas
From: Andrew Morton <akpm@linux-foundation.org>
Date: 2007-07-30 20:50:09
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On Sat, 28 Jul 2007 23:52:30 +0100 Andy Whitcroft [off-list ref] wrote:
From: Mel Gorman <redacted> Lumpy reclaim works by selecting a lead page from the LRU list and then selecting pages for reclaim from the order-aligned area of pages. In the situation were all pages in that region are inactive and not referenced by any process over time, it works well. In the situation where there is even light load on the system, the pages may not free quickly. Out of a area of 1024 pages, maybe only 950 of them are freed when the allocation attempt occurs because lumpy reclaim returned early. This patch alters the behaviour of direct reclaim for large contiguous blocks. The first attempt to call shrink_page_list() is asynchronous but if it fails, the pages are submitted a second time and the calling process waits for the IO to complete. It'll retry up to 5 times for the pages to be fully freed. This may stall allocators waiting for contiguous memory but that should be expected behaviour for high-order users. It is preferable behaviour to potentially queueing unnecessary areas for IO. Note that kswapd will not stall in this fashion.
I agree with the intent.
+/* Request for sync pageout. */
+typedef enum {
+ PAGEOUT_IO_ASYNC,
+ PAGEOUT_IO_SYNC,
+} pageout_io_t;no typedefs. (checkpatch.pl knew that ;))
quoted hunk ↗ jump to hunk
/* possible outcome of pageout() */ typedef enum { /* failed to write page out, page is locked */@@ -287,7 +293,8 @@ typedef enum { * pageout is called by shrink_page_list() for each dirty page. * Calls ->writepage(). */ -static pageout_t pageout(struct page *page, struct address_space *mapping) +static pageout_t pageout(struct page *page, struct address_space *mapping, + pageout_io_t sync_writeback) { /* * If the page is dirty, only perform writeback if that write@@ -346,6 +353,15 @@ static pageout_t pageout(struct page *page, struct address_space *mapping) ClearPageReclaim(page); return PAGE_ACTIVATE; } + + /* + * Wait on writeback if requested to. This happens when + * direct reclaiming a large contiguous area and the + * first attempt to free a ranage of pages fails
cnat tpye.
quoted hunk ↗ jump to hunk
+ */ + if (PageWriteback(page) && sync_writeback == PAGEOUT_IO_SYNC) + wait_on_page_writeback(page); + if (!PageWriteback(page)) { /* synchronous write or broken a_ops? */ ClearPageReclaim(page);@@ -423,7 +439,8 @@ cannot_free: * shrink_page_list() returns the number of reclaimed pages */ static unsigned long shrink_page_list(struct list_head *page_list, - struct scan_control *sc) + struct scan_control *sc, + pageout_io_t sync_writeback) { LIST_HEAD(ret_pages); struct pagevec freed_pvec;@@ -458,8 +475,12 @@ static unsigned long shrink_page_list(struct list_head *page_list, if (page_mapped(page) || PageSwapCache(page)) sc->nr_scanned++; - if (PageWriteback(page)) - goto keep_locked; + if (PageWriteback(page)) { + if (sync_writeback == PAGEOUT_IO_SYNC) + wait_on_page_writeback(page); + else + goto keep_locked; + }
This is unneeded and conceivably deadlocky for !__GFP_FS allocations. Probably we avoid doing all this if the test which may_enter_fs uses is false. It's unlikely that any very-high-order allocators are using GFP_NOIO or whatever, but still... -- 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/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>