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Date: Wed, 10 Apr 2024 10:47:18 +0200
From: David Hildenbrand <david@...hat.com>
To: Alex Shi <seakeel@...il.com>, alexs@...nel.org,
Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Cc: Izik Eidus <izik.eidus@...ellosystems.com>,
Matthew Wilcox <willy@...radead.org>, Andrea Arcangeli
<aarcange@...hat.com>, Hugh Dickins <hughd@...gle.com>,
Chris Wright <chrisw@...s-sol.org>
Subject: Re: [PATCH v4 8/9] mm/ksm: Convert chain series funcs and replace
get_ksm_page
On 10.04.24 05:47, Alex Shi wrote:
>
>
> On 4/9/24 7:02 PM, David Hildenbrand wrote:
>> On 09.04.24 11:28, alexs@...nel.org wrote:
>>> From: "Alex Shi (tencent)" <alexs@...nel.org>
>>>
>>> In ksm stable tree all page are single, let's convert them to use and
>>> folios as well as stable_tree_insert/stable_tree_search funcs.
>>> And replace get_ksm_page() by ksm_get_folio() since there is no more
>>> needs.
>>>
>>> It could save a few compound_head calls.
>>>
>>> Signed-off-by: Alex Shi (tencent) <alexs@...nel.org>
>>> Cc: Izik Eidus <izik.eidus@...ellosystems.com>
>>> Cc: Matthew Wilcox <willy@...radead.org>
>>> Cc: Andrea Arcangeli <aarcange@...hat.com>
>>> Cc: Hugh Dickins <hughd@...gle.com>
>>> Cc: Chris Wright <chrisw@...s-sol.org>
>>> Reviewed-by: David Hildenbrand <david@...hat.com>
>>
>> I don't recall giving that yet :)
>
> Ops...
> Sorry for misunderstand!
No worries :)
>>
>> You could have kept some get_ksm_page()->ksm_get_folio() into a separate patch.
>>
>> i.e., "[PATCH v3 11/14] mm/ksm: remove get_ksm_page and related info" from your old series could have mostly stayed separately.
>>
>
> Yes, but the 12th and 11th patches are kind of depends each other, like after merge 8,9,10,12th with get_ksm_page replaced,
>
> ../mm/ksm.c:993:21: error: ‘get_ksm_page’ defined but not used [-Werror=unused-function]
> 993 | static struct page *get_ksm_page(struct ksm_stable_node *stable_node,
> | ^~~~~~~~~~~~
>
> so we have to squash the 11th and 12th if we want to merge 12th with 8,9,10...
> or we can do just merge the 8,9,10 and keep 11th, 12th as your first suggestion?
>
I see what you mean. Including removal is certainly required there, as you remove
the last user.
It might make sense to move some cleanups+comment adjustments from
"[PATCH v3 11/14] mm/ksm: remove get_ksm_page and related info" into relevant patches.
After Patch #1 in this series, I would do
From 38a6f6017bf91d9a8869316b711b594909caa5ed Mon Sep 17 00:00:00 2001
From: David Hildenbrand <david@...hat.com>
Date: Wed, 10 Apr 2024 10:32:24 +0200
Subject: [PATCH] mm/ksm: rename get_ksm_page_flags() to ksm_get_folio_flags
As we are removing get_ksm_page_flags(), make the flags match the new
function name.
Signed-off-by: David Hildenbrand <david@...hat.com>
---
mm/ksm.c | 34 +++++++++++++++++-----------------
1 file changed, 17 insertions(+), 17 deletions(-)
diff --git a/mm/ksm.c b/mm/ksm.c
index ac080235b002..fd2666e6bda1 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -890,10 +890,10 @@ static void remove_node_from_stable_tree(struct ksm_stable_node *stable_node)
free_stable_node(stable_node);
}
-enum get_ksm_page_flags {
- GET_KSM_PAGE_NOLOCK,
- GET_KSM_PAGE_LOCK,
- GET_KSM_PAGE_TRYLOCK
+enum ksm_get_folio_flags {
+ KSM_GET_FOLIO_NOLOCK,
+ KSM_GET_FOLIO_LOCK,
+ KSM_GET_FOLIO_TRYLOCK
};
/*
@@ -916,7 +916,7 @@ enum get_ksm_page_flags {
* is on its way to being freed; but it is an anomaly to bear in mind.
*/
static struct folio *ksm_get_folio(struct ksm_stable_node *stable_node,
- enum get_ksm_page_flags flags)
+ enum ksm_get_folio_flags flags)
{
struct folio *folio;
void *expected_mapping;
@@ -959,15 +959,15 @@ static struct folio *ksm_get_folio(struct ksm_stable_node *stable_node,
goto stale;
}
- if (flags == GET_KSM_PAGE_TRYLOCK) {
+ if (flags == KSM_GET_FOLIO_TRYLOCK) {
if (!folio_trylock(folio)) {
folio_put(folio);
return ERR_PTR(-EBUSY);
}
- } else if (flags == GET_KSM_PAGE_LOCK)
+ } else if (flags == KSM_GET_FOLIO_LOCK)
folio_lock(folio);
- if (flags != GET_KSM_PAGE_NOLOCK) {
+ if (flags != KSM_GET_FOLIO_NOLOCK) {
if (READ_ONCE(folio->mapping) != expected_mapping) {
folio_unlock(folio);
folio_put(folio);
@@ -991,7 +991,7 @@ static struct folio *ksm_get_folio(struct ksm_stable_node *stable_node,
}
static struct page *get_ksm_page(struct ksm_stable_node *stable_node,
- enum get_ksm_page_flags flags)
+ enum ksm_get_folio_flags flags)
{
struct folio *folio = ksm_get_folio(stable_node, flags);
@@ -1009,7 +1009,7 @@ static void remove_rmap_item_from_tree(struct ksm_rmap_item *rmap_item)
struct page *page;
stable_node = rmap_item->head;
- page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK);
+ page = get_ksm_page(stable_node, KSM_GET_FOLIO_LOCK);
if (!page)
goto out;
@@ -1118,7 +1118,7 @@ static int remove_stable_node(struct ksm_stable_node *stable_node)
struct page *page;
int err;
- page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK);
+ page = get_ksm_page(stable_node, KSM_GET_FOLIO_LOCK);
if (!page) {
/*
* get_ksm_page did remove_node_from_stable_tree itself.
@@ -1657,7 +1657,7 @@ static struct page *stable_node_dup(struct ksm_stable_node **_stable_node_dup,
* stable_node parameter itself will be freed from
* under us if it returns NULL.
*/
- _tree_page = get_ksm_page(dup, GET_KSM_PAGE_NOLOCK);
+ _tree_page = get_ksm_page(dup, KSM_GET_FOLIO_NOLOCK);
if (!_tree_page)
continue;
nr += 1;
@@ -1780,7 +1780,7 @@ static struct page *__stable_node_chain(struct ksm_stable_node **_stable_node_du
if (!is_stable_node_chain(stable_node)) {
if (is_page_sharing_candidate(stable_node)) {
*_stable_node_dup = stable_node;
- return get_ksm_page(stable_node, GET_KSM_PAGE_NOLOCK);
+ return get_ksm_page(stable_node, KSM_GET_FOLIO_NOLOCK);
}
/*
* _stable_node_dup set to NULL means the stable_node
@@ -1886,7 +1886,7 @@ static struct page *stable_tree_search(struct page *page)
* fine to continue the walk.
*/
tree_page = get_ksm_page(stable_node_any,
- GET_KSM_PAGE_NOLOCK);
+ KSM_GET_FOLIO_NOLOCK);
}
VM_BUG_ON(!stable_node_dup ^ !!stable_node_any);
if (!tree_page) {
@@ -1947,7 +1947,7 @@ static struct page *stable_tree_search(struct page *page)
* than kpage, but that involves more changes.
*/
tree_page = get_ksm_page(stable_node_dup,
- GET_KSM_PAGE_TRYLOCK);
+ KSM_GET_FOLIO_TRYLOCK);
if (PTR_ERR(tree_page) == -EBUSY)
return ERR_PTR(-EBUSY);
@@ -2119,7 +2119,7 @@ static struct ksm_stable_node *stable_tree_insert(struct page *kpage)
* fine to continue the walk.
*/
tree_page = get_ksm_page(stable_node_any,
- GET_KSM_PAGE_NOLOCK);
+ KSM_GET_FOLIO_NOLOCK);
}
VM_BUG_ON(!stable_node_dup ^ !!stable_node_any);
if (!tree_page) {
@@ -2610,7 +2610,7 @@ static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page)
list_for_each_entry_safe(stable_node, next,
&migrate_nodes, list) {
page = get_ksm_page(stable_node,
- GET_KSM_PAGE_NOLOCK);
+ KSM_GET_FOLIO_NOLOCK);
if (page)
put_page(page);
cond_resched();
--
2.44.0
Then, adjust the get_ksm_page() comments as you change the code:
In "[PATCH v4 4/9] mm/ksm: use folio in remove_stable_node", adjust the two comments
in remove_stable_node() to state "ksm_get_folio".
In "[PATCH v4 5/9] mm/ksm: use folio in stable_node_dup", adjust the comment in
stable_node_dup().
In "[PATCH v4 8/9] mm/ksm: Convert chain series funcs and replace get_ksm_page",
adjust the comments for __stable_node_chain(), stable_tree_insert() and stable_tree_search().
Then, the remaining comments are in folio_migrate_ksm(), stable_node_dup_remove_range(),
ksm_memory_callback() and folio_migrate_flags(), and I'd just fix them up in a separate
patch after this patch here called something like "mm/ksm: update remaining comments now
that get_ksm_page() is gone".
But that's just one way of removing some "noise" from this squashed patch :)
>> [...]
>>
>>> /*
>>> @@ -1829,7 +1821,7 @@ static __always_inline struct page *chain(struct ksm_stable_node **s_n_d,
>>> * This function returns the stable tree node of identical content if found,
>>> * NULL otherwise.
>>> */
>>> -static struct page *stable_tree_search(struct page *page)
>>> +static void *stable_tree_search(struct page *page)
>>
>> There is one caller of stable_tree_search() in cmp_and_merge_page().
>>
>> Why the change from page* to void* ?
>
> Uh, a bit more changes needs if we want to remove void*.
You could keep it page* and return &folio->page, right? Then you could convert stable_tree_search() in a separate patch to return a folio* instead.
Sorry if I am missing something.
>
> diff --git a/mm/ksm.c b/mm/ksm.c
> index 0d703c3da9d8..cd414a9c33ad 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -1815,7 +1815,7 @@ static __always_inline struct folio *chain(struct ksm_stable_node **s_n_d,
> * This function returns the stable tree node of identical content if found,
> * NULL otherwise.
> */
> -static void *stable_tree_search(struct page *page)
> +static struct folio *stable_tree_search(struct page *page)
> {
> int nid;
> struct rb_root *root;
> @@ -2308,6 +2308,7 @@ static void cmp_and_merge_page(struct page *page, struct ksm_rmap_item *rmap_ite
> struct page *tree_page = NULL;
> struct ksm_stable_node *stable_node;
> struct page *kpage;
> + struct folio *folio;
> unsigned int checksum;
> int err;
> bool max_page_sharing_bypass = false;
> @@ -2333,7 +2334,8 @@ static void cmp_and_merge_page(struct page *page, struct ksm_rmap_item *rmap_ite
> }
>
> /* We first start with searching the page inside the stable tree */
> - kpage = stable_tree_search(page);
> + folio = stable_tree_search(page);
> + kpage = &folio->page;
> if (kpage == page && rmap_item->head == stable_node) {
> put_page(kpage);
> return;
>
>> I suspect cmp_and_merge_page() could similarly be converted to some degree to let kpage be a folio (separate patch).
>>
>
> Yes, there are couple of changes needed for cmp_and_merge_page() and series try_to_merge_xx_pages(), I am going to change them on the next series patches. Guess 2 phases patches are better for a big/huge one, is this right?
Smaller patches are preferable. But if we have to add temporary workarounds (like using void*), it might be better to have the relevant
cleanups part of a single patch.
--
Cheers,
David / dhildenb
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