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SubjectRe: [PATCH v1 1/2] mm/page_idle: Add support for per-pid page_idle using virtual indexing
On Mon, Jul 22, 2019 at 03:06:39PM -0700, Andrew Morton wrote:
[snip]
> > + *end = *start + count * BITS_PER_BYTE;
> > + if (*end > max_frame)
> > + *end = max_frame;
> > + return 0;
> > +}
> > +
> >
> > ...
> >
> > +static void add_page_idle_list(struct page *page,
> > + unsigned long addr, struct mm_walk *walk)
> > +{
> > + struct page *page_get;
> > + struct page_node *pn;
> > + int bit;
> > + unsigned long frames;
> > + struct page_idle_proc_priv *priv = walk->private;
> > + u64 *chunk = (u64 *)priv->buffer;
> > +
> > + if (priv->write) {
> > + /* Find whether this page was asked to be marked */
> > + frames = (addr - priv->start_addr) >> PAGE_SHIFT;
> > + bit = frames % BITMAP_CHUNK_BITS;
> > + chunk = &chunk[frames / BITMAP_CHUNK_BITS];
> > + if (((*chunk >> bit) & 1) == 0)
> > + return;
> > + }
> > +
> > + page_get = page_idle_get_page(page);
> > + if (!page_get)
> > + return;
> > +
> > + pn = kmalloc(sizeof(*pn), GFP_ATOMIC);
>
> I'm not liking this GFP_ATOMIC. If I'm reading the code correctly,
> userspace can ask for an arbitrarily large number of GFP_ATOMIC
> allocations by doing a large read. This can potentially exhaust page
> reserves which things like networking Rx interrupts need and can make
> this whole feature less reliable.

For the revision, I will pre-allocate the page nodes in advance so it does
not need to do this. Diff on top of this patch is below. Let me know any
comments, thanks.

Btw, I also dropped the idle_page_list_lock by putting the idle_page_list
list_head on the stack instead of heap.
---8<-----------------------

From: "Joel Fernandes (Google)" <joel@joelfernandes.org>
Subject: [PATCH] mm/page_idle: Avoid need for GFP_ATOMIC

GFP_ATOMIC can harm allocations does by other allocations that are in
need of reserves and the like. Pre-allocate the nodes list so that
spinlocked region can just use it.

Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
mm/page_idle.c | 19 +++++++++++++++----
1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/mm/page_idle.c b/mm/page_idle.c
index 874a60c41fef..b9c790721f16 100644
--- a/mm/page_idle.c
+++ b/mm/page_idle.c
@@ -266,6 +266,10 @@ struct page_idle_proc_priv {
unsigned long start_addr;
char *buffer;
int write;
+
+ /* Pre-allocate and provide nodes to add_page_idle_list() */
+ struct page_node *page_nodes;
+ int cur_page_node;
};

static void add_page_idle_list(struct page *page,
@@ -291,10 +295,7 @@ static void add_page_idle_list(struct page *page,
if (!page_get)
return;

- pn = kmalloc(sizeof(*pn), GFP_ATOMIC);
- if (!pn)
- return;
-
+ pn = &(priv->page_nodes[priv->cur_page_node++]);
pn->page = page_get;
pn->addr = addr;
list_add(&pn->list, &idle_page_list);
@@ -379,6 +380,15 @@ ssize_t page_idle_proc_generic(struct file *file, char __user *ubuff,
priv.buffer = buffer;
priv.start_addr = start_addr;
priv.write = write;
+
+ priv.cur_page_node = 0;
+ priv.page_nodes = kzalloc(sizeof(struct page_node) * (end_frame - start_frame),
+ GFP_KERNEL);
+ if (!priv.page_nodes) {
+ ret = -ENOMEM;
+ goto out;
+ }
+
walk.private = &priv;
walk.mm = mm;

@@ -425,6 +435,7 @@ ssize_t page_idle_proc_generic(struct file *file, char __user *ubuff,
ret = copy_to_user(ubuff, buffer, count);

up_read(&mm->mmap_sem);
+ kfree(priv.page_nodes);
out:
kfree(buffer);
out_mmput:
--
2.22.0.657.g960e92d24f-goog
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