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Date: Sun, 22 Nov 2020 20:00:19 +0800
From: Alex Shi <alex.shi@...ux.alibaba.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Hugh Dickins <hughd@...gle.com>, Yu Zhao <yuzhao@...gle.com>,
Vlastimil Babka <vbabka@...e.cz>,
Michal Hocko <mhocko@...e.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH next] mm/vmscan: __isolate_lru_page_prepare clean up
在 2020/11/21 上午7:13, Andrew Morton 写道:
> On Fri, 20 Nov 2020 16:03:33 +0800 Alex Shi <alex.shi@...ux.alibaba.com> wrote:
>
>> The function just return 2 results, so use a 'switch' to deal with its
>> result is unnecessary, and simplify it to a bool func as Vlastimil
>> suggested.
>>
>> Also removed 'goto' in using by reusing list_move().
>>
>> ...
>>
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -1540,7 +1540,7 @@ unsigned int reclaim_clean_pages_from_list(struct zone *zone,
>> */
>> int __isolate_lru_page_prepare(struct page *page, isolate_mode_t mode)
>> {
>> - int ret = -EBUSY;
>> + int ret = false;
>>
>> /* Only take pages on the LRU. */
>> if (!PageLRU(page))
>> @@ -1590,7 +1590,7 @@ int __isolate_lru_page_prepare(struct page *page, isolate_mode_t mode)
>> if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
>> return ret;
>>
>> - return 0;
>> + return true;
>> }
>
> The resulting __isolate_lru_page_prepare() is rather unpleasing.
>
> - Why return an int and not a bool?
>
> - `int ret = false' is a big hint that `ret' should have bool type!
>
> - Why not just remove `ret' and do `return false' in all those `return
> ret' places?
>
> - The __isolate_lru_page_prepare() kerneldoc still says "returns 0 on
> success, -ve errno on failure".
>
Hi Andrew,
Thanks a lot for caching and sorry for the bad patch.
It initially a 'int' version, and change it to bool in a hurry weekend.
I am sorry.
>From 36c4fbda2d55633d3c1a3e79f045cd9877453ab7 Mon Sep 17 00:00:00 2001
From: Alex Shi <alex.shi@...ux.alibaba.com>
Date: Fri, 20 Nov 2020 14:49:16 +0800
Subject: [PATCH v2 next] mm/vmscan: __isolate_lru_page_prepare clean up
The function just return 2 results, so use a 'switch' to deal with its
result is unnecessary, and simplify it to a bool func as Vlastimil
suggested.
Also remove 'goto' by reusing list_move().
Signed-off-by: Alex Shi <alex.shi@...ux.alibaba.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: Yu Zhao <yuzhao@...gle.com>
Cc: Vlastimil Babka <vbabka@...e.cz>
Cc: Michal Hocko <mhocko@...e.com>
Cc: linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org
---
mm/compaction.c | 2 +-
mm/vmscan.c | 69 +++++++++++++++++++++++--------------------------
2 files changed, 34 insertions(+), 37 deletions(-)
diff --git a/mm/compaction.c b/mm/compaction.c
index b68931854253..8d71ffebe6cb 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -988,7 +988,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
if (unlikely(!get_page_unless_zero(page)))
goto isolate_fail;
- if (__isolate_lru_page_prepare(page, isolate_mode) != 0)
+ if (!__isolate_lru_page_prepare(page, isolate_mode))
goto isolate_fail_put;
/* Try isolate the page */
diff --git a/mm/vmscan.c b/mm/vmscan.c
index c6f94e55c3fe..ab2fdee0828e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1536,19 +1536,17 @@ unsigned int reclaim_clean_pages_from_list(struct zone *zone,
* page: page to consider
* mode: one of the LRU isolation modes defined above
*
- * returns 0 on success, -ve errno on failure.
+ * returns ture on success, false on failure.
*/
-int __isolate_lru_page_prepare(struct page *page, isolate_mode_t mode)
+bool __isolate_lru_page_prepare(struct page *page, isolate_mode_t mode)
{
- int ret = -EBUSY;
-
/* Only take pages on the LRU. */
if (!PageLRU(page))
- return ret;
+ return false;
/* Compaction should not handle unevictable pages but CMA can do so */
if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE))
- return ret;
+ return false;
/*
* To minimise LRU disruption, the caller can indicate that it only
@@ -1561,7 +1559,7 @@ int __isolate_lru_page_prepare(struct page *page, isolate_mode_t mode)
if (mode & ISOLATE_ASYNC_MIGRATE) {
/* All the caller can do on PageWriteback is block */
if (PageWriteback(page))
- return ret;
+ return false;
if (PageDirty(page)) {
struct address_space *mapping;
@@ -1577,20 +1575,20 @@ int __isolate_lru_page_prepare(struct page *page, isolate_mode_t mode)
* from the page cache.
*/
if (!trylock_page(page))
- return ret;
+ return false;
mapping = page_mapping(page);
migrate_dirty = !mapping || mapping->a_ops->migratepage;
unlock_page(page);
if (!migrate_dirty)
- return ret;
+ return false;
}
}
if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
- return ret;
+ return false;
- return 0;
+ return true;
}
/*
@@ -1674,35 +1672,34 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
* only when the page is being freed somewhere else.
*/
scan += nr_pages;
- switch (__isolate_lru_page_prepare(page, mode)) {
- case 0:
+ if (!__isolate_lru_page_prepare(page, mode)) {
+ /* else it is being freed elsewhere */
+ list_move(&page->lru, src);
+ continue;
+ }
+ /*
+ * Be careful not to clear PageLRU until after we're
+ * sure the page is not being freed elsewhere -- the
+ * page release code relies on it.
+ */
+ if (unlikely(!get_page_unless_zero(page))) {
+ list_move(&page->lru, src);
+ continue;
+ }
+
+ if (!TestClearPageLRU(page)) {
/*
- * Be careful not to clear PageLRU until after we're
- * sure the page is not being freed elsewhere -- the
- * page release code relies on it.
+ * This page may in other isolation path,
+ * but we still hold lru_lock.
*/
- if (unlikely(!get_page_unless_zero(page)))
- goto busy;
-
- if (!TestClearPageLRU(page)) {
- /*
- * This page may in other isolation path,
- * but we still hold lru_lock.
- */
- put_page(page);
- goto busy;
- }
-
- nr_taken += nr_pages;
- nr_zone_taken[page_zonenum(page)] += nr_pages;
- list_move(&page->lru, dst);
- break;
-
- default:
-busy:
- /* else it is being freed elsewhere */
+ put_page(page);
list_move(&page->lru, src);
+ continue;
}
+
+ nr_taken += nr_pages;
+ nr_zone_taken[page_zonenum(page)] += nr_pages;
+ list_move(&page->lru, dst);
}
/*
--
2.29.GIT
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