From: Bob Liu <bob.liu@oracle.com>
To: Dan Streetman <ddstreet@ieee.org>
Cc: Weijie Yang <weijie.yang.kh@gmail.com>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
xen-devel@lists.xenproject.org, Mel Gorman <mgorman@suse.de>,
Hugh Dickins <hughd@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Michal Hocko <mhocko@suse.cz>,
Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>,
Shaohua Li <shli@fusionio.com>, Weijie Yang <weijieut@gmail.com>,
Linux-MM <linux-mm@kvack.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
David Vrabel <david.vrabel@citrix.com>
Subject: Re: [PATCH 1/2] swap: change swap_info singly-linked list to list_head
Date: Sun, 04 May 2014 17:39:40 +0800 [thread overview]
Message-ID: <53660ADC.8000306@oracle.com> (raw)
In-Reply-To: <CALZtONBDdo7KGKPZHuH-gHUS8ntBW+mYGPKKnh5GcQAsL5Zrfw@mail.gmail.com>
On 05/03/2014 04:00 AM, Dan Streetman wrote:
> On Fri, Apr 25, 2014 at 12:15 AM, Weijie Yang <weijie.yang.kh@gmail.com> wrote:
>> On Fri, Apr 25, 2014 at 2:48 AM, Dan Streetman <ddstreet@ieee.org> wrote:
>>> On Wed, Apr 23, 2014 at 6:34 AM, Mel Gorman <mgorman@suse.de> wrote:
>>>> On Sat, Apr 12, 2014 at 05:00:53PM -0400, Dan Streetman wrote:
> <SNIP>
>>>>> diff --git a/mm/frontswap.c b/mm/frontswap.c
>>>>> index 1b24bdc..fae1160 100644
>>>>> --- a/mm/frontswap.c
>>>>> +++ b/mm/frontswap.c
>>>>> @@ -327,15 +327,12 @@ EXPORT_SYMBOL(__frontswap_invalidate_area);
>>>>>
>>>>> static unsigned long __frontswap_curr_pages(void)
>>>>> {
>>>>> - int type;
>>>>> unsigned long totalpages = 0;
>>>>> struct swap_info_struct *si = NULL;
>>>>>
>>>>> assert_spin_locked(&swap_lock);
>>>>> - for (type = swap_list.head; type >= 0; type = si->next) {
>>>>> - si = swap_info[type];
>>>>> + list_for_each_entry(si, &swap_list_head, list)
>>>>> totalpages += atomic_read(&si->frontswap_pages);
>>>>> - }
>>>>> return totalpages;
>>>>> }
>>>>>
>>>>> @@ -347,11 +344,9 @@ static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused,
>>>>> int si_frontswap_pages;
>>>>> unsigned long total_pages_to_unuse = total;
>>>>> unsigned long pages = 0, pages_to_unuse = 0;
>>>>> - int type;
>>>>>
>>>>> assert_spin_locked(&swap_lock);
>>>>> - for (type = swap_list.head; type >= 0; type = si->next) {
>>>>> - si = swap_info[type];
>>>>> + list_for_each_entry(si, &swap_list_head, list) {
>>>>> si_frontswap_pages = atomic_read(&si->frontswap_pages);
>>>>> if (total_pages_to_unuse < si_frontswap_pages) {
>>>>> pages = pages_to_unuse = total_pages_to_unuse;
>>>>
>>>> The frontswap shrink code looks suspicious. If the target is smaller than
>>>> the total number of frontswap pages then it does nothing. The callers
__frontswap_unuse_pages() is called only to get the correct value of
pages_to_unuse which will pass to try_to_unuse(), perhaps we should
rename it to __frontswap_unuse_pages_nr()..
------
ret = __frontswap_shrink(target_pages, &pages_to_unuse, &type);
-> __frontswap_unuse_pages(total_pages_to_unuse, pages_to_unuse, type);
try_to_unuse(type, true, pages_to_unuse);
------
>>>> appear to get this right at least. Similarly, if the first swapfile has
>>>> fewer frontswap pages than the target then it does not unuse the target
>>>> number of pages because it only handles one swap file. It's outside the
>>>> scope of your patch to address this or wonder if xen balloon driver is
>>>> really using it the way it's expected.
>>>
>>> I didn't look into the frontswap shrinking code, but I agree the
>>> existing logic there doesn't look right. I'll review frontswap in
>>> more detail to see if it needs changing here, unless anyone else gets
>>> it to first :-)
>>>
>>
>> FYI, I drop the frontswap_shrink code in a patch
>> see: https://lkml.org/lkml/2014/1/27/98
>
> frontswap_shrink() is actually used (only) by drivers/xen/xen-selfballoon.c.
>
> However, I completely agree with you that the backend should be doing
> the shrinking, not from a frontswap api. Forcing frontswap to shrink
> is backwards - xen-selfballoon appears to be assuming that xem/tmem is
> the only possible frontswap backend. It certainly doensn't make any
> sense for xen-selfballoon to force zswap to shrink itself, does it?
>
> If xen-selfballoon wants to shrink its frontswap backend tmem, it
> should do that by telling tmem directly to shrink itself (which it
> looks like tmem would have to implement, just like zswap sends its LRU
> pages back to swapcache when it becomes full).
>
Yes, it's possible in theory, but tmem is located in xen(host) which
can't put back pages to swap cache(in guest os) directly. Use
frontswap_shrink() can make things simple and easier.
And I think frontswap shrink isn't a blocker of this patch set, so
please keep it.
--
Regards,
-Bob
next prev parent reply other threads:[~2014-05-04 9:40 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-13 10:42 [PATCH] mm: swap: Use swapfiles in priority order Mel Gorman
2014-02-13 15:58 ` Weijie Yang
2014-02-14 10:17 ` Mel Gorman
2014-02-14 13:33 ` Weijie Yang
[not found] ` <loom.20140214T135753-812@post.gmane.org>
[not found] ` <CABdxLJHS5kw0rpD=+77iQtc6PMeRXoWnh-nh5VzjjfGHJ5wLGQ@mail.gmail.com>
2014-02-24 8:28 ` Hugh Dickins
2014-04-12 21:00 ` [PATCH 0/2] swap: simplify/fix swap_list handling and iteration Dan Streetman
2014-04-12 21:00 ` [PATCH 1/2] swap: change swap_info singly-linked list to list_head Dan Streetman
2014-04-23 10:34 ` Mel Gorman
2014-04-24 0:17 ` Shaohua Li
2014-04-24 8:30 ` Mel Gorman
2014-04-24 18:48 ` Dan Streetman
2014-04-25 4:15 ` Weijie Yang
2014-05-02 20:00 ` Dan Streetman
2014-05-04 9:39 ` Bob Liu [this message]
2014-05-04 20:16 ` Dan Streetman
2014-04-25 8:38 ` Mel Gorman
2014-04-12 21:00 ` [PATCH 2/2] swap: use separate priority list for available swap_infos Dan Streetman
2014-04-23 13:14 ` Mel Gorman
2014-04-24 17:52 ` Dan Streetman
2014-04-25 8:49 ` Mel Gorman
2014-05-02 19:02 ` [PATCHv2 0/4] swap: simplify/fix swap_list handling and iteration Dan Streetman
2014-05-02 19:02 ` [PATCHv2 1/4] swap: change swap_info singly-linked list to list_head Dan Streetman
2014-05-02 19:02 ` [PATCH 2/4] plist: add helper functions Dan Streetman
2014-05-12 10:35 ` Mel Gorman
2014-05-02 19:02 ` [PATCH 3/4] plist: add plist_rotate Dan Streetman
2014-05-06 2:18 ` Steven Rostedt
2014-05-06 20:12 ` Dan Streetman
2014-05-06 20:39 ` Steven Rostedt
2014-05-06 21:47 ` Dan Streetman
2014-05-06 22:43 ` Steven Rostedt
2014-05-02 19:02 ` [PATCH 4/4] swap: change swap_list_head to plist, add swap_avail_head Dan Streetman
2014-05-05 15:51 ` Dan Streetman
2014-05-05 19:13 ` Steven Rostedt
2014-05-05 19:38 ` Peter Zijlstra
2014-05-09 20:42 ` [PATCH] plist: make CONFIG_DEBUG_PI_LIST selectable Dan Streetman
2014-05-09 21:17 ` Steven Rostedt
2014-05-12 11:11 ` [PATCH 4/4] swap: change swap_list_head to plist, add swap_avail_head Mel Gorman
2014-05-12 13:00 ` Dan Streetman
2014-05-12 16:38 ` [PATCHv3 0/4] swap: simplify/fix swap_list handling and iteration Dan Streetman
2014-05-12 16:38 ` [PATCHv2 1/4] swap: change swap_info singly-linked list to list_head Dan Streetman
2014-05-12 16:38 ` [PATCH 2/4] plist: add helper functions Dan Streetman
2014-05-12 16:38 ` [PATCHv2 3/4] plist: add plist_requeue Dan Streetman
2014-05-13 10:33 ` Mel Gorman
2014-05-12 16:38 ` [PATCHv2 4/4] swap: change swap_list_head to plist, add swap_avail_head Dan Streetman
2014-05-13 10:34 ` Mel Gorman
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=53660ADC.8000306@oracle.com \
--to=bob.liu@oracle.com \
--cc=akpm@linux-foundation.org \
--cc=boris.ostrovsky@oracle.com \
--cc=david.vrabel@citrix.com \
--cc=ddstreet@ieee.org \
--cc=ehrhardt@linux.vnet.ibm.com \
--cc=hughd@google.com \
--cc=konrad.wilk@oracle.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mgorman@suse.de \
--cc=mhocko@suse.cz \
--cc=shli@fusionio.com \
--cc=weijie.yang.kh@gmail.com \
--cc=weijieut@gmail.com \
--cc=xen-devel@lists.xenproject.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).