Messages in this thread Patch in this message | | | Date | Wed, 16 Nov 2005 14:44:50 -0800 | From | Andrew Morton <> | Subject | Re: mmap over nfs leads to excessive system load |
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Trond Myklebust <trond.myklebust@fys.uio.no> wrote: > > On Wed, 2005-11-16 at 14:10 -0800, Andrew Morton wrote: > > > > How is the filesystem supposed to distinguish between the cases > > > "VM->writepage()", and "VM->writepages->mpage_writepages->writepage()"? > > > > > > > Via the writeback_control, hopefully. > > > > For write_one_page(), sync_mode==WB_SYNC_ALL, so NFS should start the I/O > > immediately (it appears to not do so). > > Sorry, but so does filemap_fdatawrite(). WB_SYNC_ALL clearly does not > discriminate between a writepages() and a single writepage() situation, > whatever the original intention was.
Could peek at wbc->nr_pages, or add another boolean to writeback_control for this.
diff -puN include/linux/writeback.h~writeback_control-flag-writepages include/linux/writeback.h --- devel/include/linux/writeback.h~writeback_control-flag-writepages 2005-11-16 14:43:52.000000000 -0800 +++ devel-akpm/include/linux/writeback.h 2005-11-16 14:43:52.000000000 -0800 @@ -53,10 +53,11 @@ struct writeback_control { loff_t start; loff_t end; - unsigned nonblocking:1; /* Don't get stuck on request queues */ - unsigned encountered_congestion:1; /* An output: a queue is full */ - unsigned for_kupdate:1; /* A kupdate writeback */ - unsigned for_reclaim:1; /* Invoked from the page allocator */ + unsigned nonblocking:1; /* Don't get stuck on request queues */ + unsigned encountered_congestion:1; /* An output: a queue is full */ + unsigned for_kupdate:1; /* A kupdate writeback */ + unsigned for_reclaim:1; /* Invoked from the page allocator */ + unsigned for_writepages:1; /* This is a writepages() call */ }; /* diff -puN mm/page-writeback.c~writeback_control-flag-writepages mm/page-writeback.c --- devel/mm/page-writeback.c~writeback_control-flag-writepages 2005-11-16 14:43:52.000000000 -0800 +++ devel-akpm/mm/page-writeback.c 2005-11-16 14:43:52.000000000 -0800 @@ -550,11 +550,17 @@ void __init page_writeback_init(void) int do_writepages(struct address_space *mapping, struct writeback_control *wbc) { + int ret; + if (wbc->nr_to_write <= 0) return 0; + wbc->for_writepages = 1; if (mapping->a_ops->writepages) - return mapping->a_ops->writepages(mapping, wbc); - return generic_writepages(mapping, wbc); + ret = mapping->a_ops->writepages(mapping, wbc); + else + ret = generic_writepages(mapping, wbc); + wbc->for_writepages = 0; + return ret; } /** _ > > For vmscan->writepage, wbc->for_reclaim is set, so we know that the IO > > should be pushed immediately. nfs_writepage() seems to dtrt here. > > > > With the proposed changes, we don't need that iput() in nfs_writepage(). > > That worries me because I recall from a couple of years back that there are > > really subtle races with doing iput() on the vmscan->writepage() path. > > Cannot remember what they were though... > > Possibly to do with block filesystems that may trigger ->writepage() > while inside iput_final()? NFS can't do that.
iput_final() can call truncate_inode_pages - maybe it was a deadlock, but I'm fairly sure it was a race. - 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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