Messages in this thread Patch in this message | | | Date | Sun, 16 Jun 2002 23:53:51 -0700 | From | Andrew Morton <> | Subject | [patch 18/19] allow GFP_NOFS allocators to perform swapcache writeout |
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(Requires the direct-to-BIO-for-swap patch)
One weakness which was introduced when the buffer LRU went away was that GFP_NOFS allocations became equivalent to GFP_NOIO. Because all writeback goes via writepage/writepages, which requires entry into the filesystem.
However now that swapout no longer calls bmap(), we can honour GFP_NOFS's intent for swapcache pages. So if the allocation request specifies __GFP_IO and !__GFP_FS, we can wait on swapcache pages and we can perform swapcache writeout.
This should strengthen the VM somewhat.
--- 2.5.22/mm/vmscan.c~GFP_IO-swap Sun Jun 16 23:12:53 2002 +++ 2.5.22-akpm/mm/vmscan.c Sun Jun 16 23:12:53 2002 @@ -391,7 +391,8 @@ shrink_cache(int nr_pages, zone_t *class spin_lock(&pagemap_lru_lock); while (--max_scan >= 0 && (entry = inactive_list.prev) != &inactive_list) { - struct page * page; + struct page *page; + int may_enter_fs; if (need_resched()) { spin_unlock(&pagemap_lru_lock); @@ -426,10 +427,17 @@ shrink_cache(int nr_pages, zone_t *class goto page_mapped; /* + * swap activity never enters the filesystem and is safe + * for GFP_NOFS allocations. + */ + may_enter_fs = (gfp_mask & __GFP_FS) || + (PageSwapCache(page) && (gfp_mask & __GFP_IO)); + + /* * IO in progress? Leave it at the back of the list. */ if (unlikely(PageWriteback(page))) { - if (gfp_mask & __GFP_FS) { + if (may_enter_fs) { page_cache_get(page); spin_unlock(&pagemap_lru_lock); wait_on_page_writeback(page); @@ -450,7 +458,7 @@ shrink_cache(int nr_pages, zone_t *class mapping = page->mapping; if (PageDirty(page) && is_page_cache_freeable(page) && - page->mapping && (gfp_mask & __GFP_FS)) { + page->mapping && may_enter_fs) { /* * It is not critical here to write it only if * the page is unmapped beause any direct writer @@ -479,6 +487,15 @@ shrink_cache(int nr_pages, zone_t *class * If the page has buffers, try to free the buffer mappings * associated with this page. If we succeed we try to free * the page as well. + * + * We do this even if the page is PageDirty(). + * try_to_release_page() does not perform I/O, but it is + * possible for a page to have PageDirty set, but it is actually + * clean (all its buffers are clean). This happens if the + * buffers were written out directly, with submit_bh(). ext3 + * will do this, as well as the blockdev mapping. + * try_to_release_page() will discover that cleanness and will + * drop the buffers and mark the page clean - it can be freed. */ if (PagePrivate(page)) { spin_unlock(&pagemap_lru_lock); - - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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