From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx119.postini.com [74.125.245.119]) by kanga.kvack.org (Postfix) with SMTP id 9A7C16B0005 for ; Mon, 8 Apr 2013 17:17:13 -0400 (EDT) Date: Mon, 8 Apr 2013 14:17:10 -0700 From: Andrew Morton Subject: Re: [PATCH] mm: remove compressed copy from zram in-memory Message-Id: <20130408141710.1a1f76a0054bba49a42c76ca@linux-foundation.org> In-Reply-To: <1365400862-9041-1-git-send-email-minchan@kernel.org> References: <1365400862-9041-1-git-send-email-minchan@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Minchan Kim Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Hugh Dickins , Seth Jennings , Nitin Gupta , Konrad Rzeszutek Wilk , Shaohua Li , Dan Magenheimer On Mon, 8 Apr 2013 15:01:02 +0900 Minchan Kim wrote: > Swap subsystem does lazy swap slot free with expecting the page > would be swapped out again so we can avoid unnecessary write. Is that correct? How can it save a write? > But the problem in in-memory swap(ex, zram) is that it consumes > memory space until vm_swap_full(ie, used half of all of swap device) > condition meet. It could be bad if we use multiple swap device, > small in-memory swap and big storage swap or in-memory swap alone. > > This patch makes swap subsystem free swap slot as soon as swap-read > is completed and make the swapcache page dirty so the page should > be written out the swap device to reclaim it. > It means we never lose it. >>From my reading of the patch, that isn't how it works? It changed end_swap_bio_read() to call zram_slot_free_notify(), which appears to free the underlying compressed page. I have a feeling I'm hopelessly confused. > --- a/mm/page_io.c > +++ b/mm/page_io.c > @@ -20,6 +20,7 @@ > #include > #include > #include > +#include > #include > > static struct bio *get_swap_bio(gfp_t gfp_flags, > @@ -81,8 +82,30 @@ void end_swap_bio_read(struct bio *bio, int err) > iminor(bio->bi_bdev->bd_inode), > (unsigned long long)bio->bi_sector); > } else { > + /* > + * There is no reason to keep both uncompressed data and > + * compressed data in memory. > + */ > + struct swap_info_struct *sis; > + > SetPageUptodate(page); > + sis = page_swap_info(page); > + if (sis->flags & SWP_BLKDEV) { > + struct gendisk *disk = sis->bdev->bd_disk; > + if (disk->fops->swap_slot_free_notify) { > + swp_entry_t entry; > + unsigned long offset; > + > + entry.val = page_private(page); > + offset = swp_offset(entry); > + > + SetPageDirty(page); > + disk->fops->swap_slot_free_notify(sis->bdev, > + offset); > + } > + } > } > + > unlock_page(page); > bio_put(bio); The new code is wasted space if CONFIG_BLOCK=n, yes? Also, what's up with the SWP_BLKDEV test? zram doesn't support SWP_FILE? Why on earth not? Putting swap_slot_free_notify() into block_device_operations seems rather wrong. It precludes zram-over-swapfiles for all time and means that other subsystems cannot get notifications for swap slot freeing for swapfile-backed swap. -- 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: email@kvack.org