From: John Hubbard <jhubbard@nvidia.com>
To: Minchan Kim <minchan@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>
Cc: kernel-team@lge.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org,
Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@suse.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Subject: Re: [RFC 08/11] mm: make ttu's return boolean
Date: Tue, 7 Mar 2017 23:13:26 -0800 [thread overview]
Message-ID: <70f60783-e098-c1a9-11b4-544530bcd809@nvidia.com> (raw)
In-Reply-To: <1488436765-32350-9-git-send-email-minchan@kernel.org>
On 03/01/2017 10:39 PM, Minchan Kim wrote:
> try_to_unmap returns SWAP_SUCCESS or SWAP_FAIL so it's suitable for
> boolean return. This patch changes it.
Hi Minchan,
So, up until this patch, I definitely like the cleanup, because as you observed, the
return values didn't need so many different values. However, at this point, I think
you should stop, and keep the SWAP_SUCCESS and SWAP_FAIL (or maybe even rename them
to UNMAP_* or TTU_RESULT_*, to match their functions' names better), because
removing them makes the code considerably less readable.
And since this is billed as a cleanup, we care here, even though this is a minor
point. :)
Bool return values are sometimes perfect, such as when asking a question:
bool mode_changed = needs_modeset(crtc_state);
The above is very nice. However, for returning success or failure, bools are not as
nice, because *usually* success == true, except when you use the errno-based system,
in which success == 0 (which would translate to false, if you mistakenly treated it
as a bool). That leads to the reader having to remember which system is in use,
usually with no visual cues to help.
>
[...]
> if (PageSwapCache(p)) {
> @@ -971,7 +971,7 @@ static int hwpoison_user_mappings(struct page *p, unsigned long pfn,
> collect_procs(hpage, &tokill, flags & MF_ACTION_REQUIRED);
>
> ret = try_to_unmap(hpage, ttu);
> - if (ret != SWAP_SUCCESS)
> + if (!ret)
> pr_err("Memory failure: %#lx: failed to unmap page (mapcount=%d)\n",
> pfn, page_mapcount(hpage));
>
> @@ -986,8 +986,7 @@ static int hwpoison_user_mappings(struct page *p, unsigned long pfn,
> * any accesses to the poisoned memory.
> */
> forcekill = PageDirty(hpage) || (flags & MF_MUST_KILL);
> - kill_procs(&tokill, forcekill, trapno,
> - ret != SWAP_SUCCESS, p, pfn, flags);
> + kill_procs(&tokill, forcekill, trapno, !ret , p, pfn, flags);
The kill_procs() invocation was a little more readable before.
>
[...]
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 170c61f..e4b74f1 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -966,7 +966,6 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> int may_enter_fs;
> enum page_references references = PAGEREF_RECLAIM_CLEAN;
> bool dirty, writeback;
> - int ret = SWAP_SUCCESS;
>
> cond_resched();
>
> @@ -1139,13 +1138,9 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> * processes. Try to unmap it here.
> */
> if (page_mapped(page)) {
> - switch (ret = try_to_unmap(page,
> - ttu_flags | TTU_BATCH_FLUSH)) {
> - case SWAP_FAIL:
Again: the SWAP_FAIL makes it crystal clear which case we're in.
I also wonder if UNMAP_FAIL or TTU_RESULT_FAIL is a better name?
thanks,
John Hubbard
NVIDIA
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next prev parent reply other threads:[~2017-03-08 7:20 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-02 6:39 [RFC 00/11] make try_to_unmap simple Minchan Kim
2017-03-02 6:39 ` [RFC 01/11] mm: use SWAP_SUCCESS instead of 0 Minchan Kim
2017-03-02 14:27 ` Anshuman Khandual
2017-03-03 3:01 ` Minchan Kim
2017-03-06 9:07 ` Anshuman Khandual
2017-03-07 14:19 ` Kirill A. Shutemov
2017-03-08 6:25 ` Minchan Kim
2017-03-02 6:39 ` [RFC 02/11] mm: remove unncessary ret in page_referenced Minchan Kim
2017-03-02 14:33 ` Anshuman Khandual
2017-03-03 3:03 ` Minchan Kim
2017-03-07 14:20 ` Kirill A. Shutemov
2017-03-02 6:39 ` [RFC 03/11] mm: remove SWAP_DIRTY in ttu Minchan Kim
2017-03-02 7:34 ` Hillf Danton
2017-03-03 2:57 ` Minchan Kim
2017-03-02 14:42 ` Anshuman Khandual
2017-03-07 14:20 ` Kirill A. Shutemov
2017-03-02 6:39 ` [RFC 04/11] mm: remove SWAP_MLOCK check for SWAP_SUCCESS " Minchan Kim
2017-03-02 14:51 ` Anshuman Khandual
2017-03-03 3:04 ` Minchan Kim
2017-03-07 14:26 ` Kirill A. Shutemov
2017-03-08 6:40 ` Minchan Kim
2017-03-02 6:39 ` [RFC 05/11] mm: make the try_to_munlock void function Minchan Kim
2017-03-03 11:43 ` Anshuman Khandual
2017-03-06 2:09 ` Minchan Kim
2017-03-06 9:40 ` Anshuman Khandual
2017-03-07 6:50 ` Minchan Kim
2017-03-07 8:55 ` Anshuman Khandual
2017-03-07 15:17 ` Kirill A. Shutemov
2017-03-08 6:41 ` Minchan Kim
2017-03-02 6:39 ` [RFC 06/11] mm: remove SWAP_MLOCK in ttu Minchan Kim
2017-03-03 12:36 ` Anshuman Khandual
2017-03-06 2:15 ` Minchan Kim
2017-03-07 15:24 ` Kirill A. Shutemov
2017-03-08 6:42 ` Minchan Kim
2017-03-02 6:39 ` [RFC 07/11] mm: remove SWAP_AGAIN " Minchan Kim
2017-03-03 12:54 ` Anshuman Khandual
2017-03-06 2:16 ` Minchan Kim
2017-03-02 6:39 ` [RFC 08/11] mm: make ttu's return boolean Minchan Kim
2017-03-08 7:13 ` John Hubbard [this message]
2017-03-09 6:37 ` Minchan Kim
2017-03-09 6:46 ` John Hubbard
2017-03-02 6:39 ` [RFC 09/11] mm: make rmap_walk void function Minchan Kim
2017-03-02 6:39 ` [RFC 10/11] mm: make rmap_one boolean function Minchan Kim
2017-03-02 6:39 ` [RFC 11/11] mm: remove SWAP_[SUCCESS|AGAIN|FAIL] Minchan Kim
2017-03-03 13:04 ` Anshuman Khandual
2017-03-06 2:18 ` Minchan Kim
2017-03-02 14:22 ` [RFC 00/11] make try_to_unmap simple Anshuman Khandual
2017-03-03 2:11 ` Minchan Kim
2017-03-03 5:39 ` Anshuman Khandual
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