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Date: Tue, 29 Jan 2013 08:46:46 +0900
From: Minchan Kim <minchan@...nel.org>
To: Seth Jennings <sjenning@...ux.vnet.ibm.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Nitin Gupta <ngupta@...are.org>,
Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
Dan Magenheimer <dan.magenheimer@...cle.com>,
Robert Jennings <rcj@...ux.vnet.ibm.com>,
Jenifer Hopper <jhopper@...ibm.com>,
Mel Gorman <mgorman@...e.de>,
Johannes Weiner <jweiner@...hat.com>,
Rik van Riel <riel@...hat.com>,
Larry Woodman <lwoodman@...hat.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org
Subject: Re: [PATCHv2 7/9] mm: break up swap_writepage() for frontswap
backends
On Mon, Jan 28, 2013 at 11:26:43AM -0600, Seth Jennings wrote:
> On 01/27/2013 10:22 PM, Minchan Kim wrote:
> > On Mon, Jan 07, 2013 at 02:24:38PM -0600, Seth Jennings wrote:
> >> swap_writepage() is currently where frontswap hooks into the swap
> >> write path to capture pages with the frontswap_store() function.
> >> However, if a frontswap backend wants to "resume" the writeback of
> >> a page to the swap device, it can't call swap_writepage() as
> >> the page will simply reenter the backend.
> >>
> >> This patch separates swap_writepage() into a top and bottom half, the
> >> bottom half named __swap_writepage() to allow a frontswap backend,
> >> like zswap, to resume writeback beyond the frontswap_store() hook and
> >> by notified when the writeback completes.
> >>
> >> Signed-off-by: Seth Jennings <sjenning@...ux.vnet.ibm.com>
> >
> > Looks good to me except few nitpicks.
>
> I broke these changes out from the main zswap patch (patch 8/9) in
> response to a request for Dan. You are right in that there are
> changes here unrelated to the commit message.
>
> The other changes are related to allowing zswap to do accounting on
> the number of outstanding flushes to the swap device.
>
> If I'm going to break those out though the two resulting patches would be:
> 1. breakup __swap_writepage() and un-static __add_to_swap_cache() to
> allow resuming of swap page writeback
> 2. change __swap_writepage() signature to include end_write_func and
> un-static end_swap_bio_write() for accounting of outstanding flushes
>
Or please add comment why you want to export some functions.
Thanks!
> Is that what you'd like to see?
>
> Seth
>
> >
> > Acked-by: Minchan Kim <minchan@...nel.org>
> >
> >> ---
> >> include/linux/swap.h | 4 ++++
> >> mm/page_io.c | 22 +++++++++++++++++-----
> >> mm/swap_state.c | 2 +-
> >> 3 files changed, 22 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/include/linux/swap.h b/include/linux/swap.h
> >> index 8c66486..a3da829 100644
> >> --- a/include/linux/swap.h
> >> +++ b/include/linux/swap.h
> >> @@ -321,6 +321,9 @@ static inline void mem_cgroup_uncharge_swap(swp_entry_t ent)
> >> /* linux/mm/page_io.c */
> >> extern int swap_readpage(struct page *);
> >> extern int swap_writepage(struct page *page, struct writeback_control *wbc);
> >> +extern void end_swap_bio_write(struct bio *bio, int err);
> >> +extern int __swap_writepage(struct page *page, struct writeback_control *wbc,
> >> + void (*end_write_func)(struct bio *, int));
> >> extern int swap_set_page_dirty(struct page *page);
> >> extern void end_swap_bio_read(struct bio *bio, int err);
> >>
> >> @@ -335,6 +338,7 @@ extern struct address_space swapper_space;
> >> extern void show_swap_cache_info(void);
> >> extern int add_to_swap(struct page *);
> >> extern int add_to_swap_cache(struct page *, swp_entry_t, gfp_t);
> >> +extern int __add_to_swap_cache(struct page *page, swp_entry_t entry);
> >
> > What's related __add_to_swap_cache with this patch?
> >
> >> extern void __delete_from_swap_cache(struct page *);
> >> extern void delete_from_swap_cache(struct page *);
> >> extern void free_page_and_swap_cache(struct page *);
> >> diff --git a/mm/page_io.c b/mm/page_io.c
> >> index c535d39..806085e 100644
> >> --- a/mm/page_io.c
> >> +++ b/mm/page_io.c
> >> @@ -43,7 +43,7 @@ static struct bio *get_swap_bio(gfp_t gfp_flags,
> >> return bio;
> >> }
> >>
> >> -static void end_swap_bio_write(struct bio *bio, int err)
> >> +void end_swap_bio_write(struct bio *bio, int err)
> >
> > Why do you remove static in this patch? It's not related to the patch.
> >
> >> {
> >> const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
> >> struct page *page = bio->bi_io_vec[0].bv_page;
> >> @@ -180,15 +180,16 @@ bad_bmap:
> >> goto out;
> >> }
> >>
> >> +int __swap_writepage(struct page *page, struct writeback_control *wbc,
> >> + void (*end_write_func)(struct bio *, int));
> >> +
> >> /*
> >> * We may have stale swap cache pages in memory: notice
> >> * them here and get rid of the unnecessary final write.
> >> */
> >> int swap_writepage(struct page *page, struct writeback_control *wbc)
> >> {
> >> - struct bio *bio;
> >> - int ret = 0, rw = WRITE;
> >> - struct swap_info_struct *sis = page_swap_info(page);
> >> + int ret = 0;
> >>
> >> if (try_to_free_swap(page)) {
> >> unlock_page(page);
> >> @@ -200,6 +201,17 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
> >> end_page_writeback(page);
> >> goto out;
> >> }
> >> + ret = __swap_writepage(page, wbc, end_swap_bio_write);
> >> +out:
> >> + return ret;
> >> +}
> >> +
> >> +int __swap_writepage(struct page *page, struct writeback_control *wbc,
> >> + void (*end_write_func)(struct bio *, int))
> >> +{
> >> + struct bio *bio;
> >> + int ret = 0, rw = WRITE;
> >> + struct swap_info_struct *sis = page_swap_info(page);
> >>
> >> if (sis->flags & SWP_FILE) {
> >> struct kiocb kiocb;
> >> @@ -227,7 +239,7 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
> >> return ret;
> >> }
> >>
> >> - bio = get_swap_bio(GFP_NOIO, page, end_swap_bio_write);
> >> + bio = get_swap_bio(GFP_NOIO, page, end_write_func);
> >> if (bio == NULL) {
> >> set_page_dirty(page);
> >> unlock_page(page);
> >> diff --git a/mm/swap_state.c b/mm/swap_state.c
> >> index 0cb36fb..7eded9c 100644
> >> --- a/mm/swap_state.c
> >> +++ b/mm/swap_state.c
> >> @@ -67,7 +67,7 @@ void show_swap_cache_info(void)
> >> * __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
> >> * but sets SwapCache flag and private instead of mapping and index.
> >> */
> >> -static int __add_to_swap_cache(struct page *page, swp_entry_t entry)
> >> +int __add_to_swap_cache(struct page *page, swp_entry_t entry)
> >
> > Ditto
> >
> >> {
> >> int error;
> >>
> >> --
> >> 1.7.9.5
> >>
> >> --
> >> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> >> the body to majordomo@...ck.org. For more info on Linux MM,
> >> see: http://www.linux-mm.org/ .
> >> Don't email: <a href=mailto:"dont@...ck.org"> email@...ck.org </a>
> >
>
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@...ck.org. For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@...ck.org"> email@...ck.org </a>
--
Kind regards,
Minchan Kim
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