There were some reported problems in the past about trashing page cache when a backup software (i.e., rsync) touches a huge amount of pages (see for example [1]). This problem has been almost fixed by the Minchan Kim's patch [2] and a proper use of fadvise() in the backup software. For example this patch set [3] has been proposed for inclusion in rsync. However, there can be still other similar trashing problems: when the backup software reads all the source files, some of them may be part of the actual working set of the system. When a POSIX_FADV_DONTNEED is performed _all_ pages are evicted from pagecache, both the working set and the use-once pages touched only by the backup software. A previous proposal [4] tried to resolve this problem being less agressive in invalidating active pages, moving them to the inactive list intead of just evict them from the page cache. However, this approach changed completely the old behavior of invalidate_mapping_pages(), that is not only used by fadvise. The new solution maps POSIX_FADV_NOREUSE to the less-agressive page invalidation policy. With POSIX_FADV_NOREUSE active pages are moved to the tail of the inactive list, and pages in the inactive list are just removed from page cache. Pages mapped by other processes or unevictable pages are not touched at all. In this way if the backup was the only user of a page, that page will be immediately removed from the page cache by calling POSIX_FADV_NOREUSE. If the page was also touched by other tasks it'll be moved to the inactive list, having another chance of being re-added to the working set, or simply reclaimed when memory is needed. In conclusion, now userspace applications that want to drop some page cache pages can choose between the following advices: POSIX_FADV_DONTNEED = drop page cache if possible POSIX_FADV_NOREUSE = reduce page cache eligibility [1] http://marc.info/?l=rsync&m=128885034930933&w=2 [2] https://lkml.org/lkml/2011/2/20/57 [3] http://lists.samba.org/archive/rsync/2010-November/025827.html [4] https://lkml.org/lkml/2011/6/23/35 Signed-off-by: Andrea Righi <andrea@xxxxxxxxxxxxxxx> --- mm/fadvise.c | 11 ++++++----- 1 files changed, 6 insertions(+), 5 deletions(-) diff --git a/mm/fadvise.c b/mm/fadvise.c index 8d723c9..bcc79ac 100644 --- a/mm/fadvise.c +++ b/mm/fadvise.c @@ -33,7 +33,7 @@ SYSCALL_DEFINE(fadvise64_64)(int fd, loff_t offset, loff_t len, int advice) pgoff_t start_index; pgoff_t end_index; unsigned long nrpages; - int ret = 0; + int ret = 0, force = true; if (!file) return -EBADF; @@ -106,7 +106,7 @@ SYSCALL_DEFINE(fadvise64_64)(int fd, loff_t offset, loff_t len, int advice) nrpages = end_index - start_index + 1; if (!nrpages) nrpages = ~0UL; - + ret = force_page_cache_readahead(mapping, file, start_index, nrpages); @@ -114,7 +114,8 @@ SYSCALL_DEFINE(fadvise64_64)(int fd, loff_t offset, loff_t len, int advice) ret = 0; break; case POSIX_FADV_NOREUSE: - break; + /* Reduce cache eligibility */ + force = false; case POSIX_FADV_DONTNEED: if (!bdi_write_congested(mapping->backing_dev_info)) filemap_flush(mapping); @@ -124,8 +125,8 @@ SYSCALL_DEFINE(fadvise64_64)(int fd, loff_t offset, loff_t len, int advice) end_index = (endbyte >> PAGE_CACHE_SHIFT); if (end_index >= start_index) - invalidate_mapping_pages(mapping, start_index, - end_index); + __invalidate_mapping_pages(mapping, start_index, + end_index, force); break; default: ret = -EINVAL; -- 1.7.4.1 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>