From: "Juan M. de la Torre" <jmtorre@gmx.net>
To: linux-kernel@vger.kernel.org
Subject: Possible bug in __alloc_pages() ?
Date: Tue, 17 Sep 2002 23:48:04 +0200 [thread overview]
Message-ID: <20020917214804.GA891@apocalipsis> (raw)
Hi, this code appears at the beggining of __page_alloc() (kernel 2.4.19):
min = 1UL << order;
for (;;) {
zone_t *z = *(zone++);
if (!z)
break;
min += z->pages_low;
if (z->free_pages > min) {
page = rmqueue(z, order);
if (page)
return page;
}
}
AFAIK, what this code does is to try to alloc the requested pages from
the first zone in a zone_list (passed as argument) which have enought free
pages.
A zone is considered to have enought free pages if z->free_pages is greater
than (number_of_requested_pages + z->pages_low).
In the loop shown, the first iteration is OK, but in the second iteration
(which only occurs if the first zone in the zone_list hasn't enought free
pages) the zone will only be considered to have enought free pages if
z->free_pages is greater that (number_of_requested_pages + z->pages_low
+ PREV_ZONE->pages_low).
I think this is a bug, but i'm not sure (i'm not a VM hacker).
If it is a bug, there are other two loops in the same function which
are buggy.
Possible patch:
--- linux/mm/page_alloc.c.orig Tue Sep 17 23:45:02 2002
+++ linux/mm/page_alloc.c Tue Sep 17 23:46:45 2002
@@ -330,8 +330,7 @@
if (!z)
break;
- min += z->pages_low;
- if (z->free_pages > min) {
+ if (z->free_pages > min + z->pages_low) {
page = rmqueue(z, order);
if (page)
return page;
@@ -354,8 +353,8 @@
local_min = z->pages_min;
if (!(gfp_mask & __GFP_WAIT))
local_min >>= 2;
- min += local_min;
- if (z->free_pages > min) {
+
+ if (z->free_pages > min + local_min) {
page = rmqueue(z, order);
if (page)
return page;
@@ -394,8 +393,7 @@
if (!z)
break;
- min += z->pages_min;
- if (z->free_pages > min) {
+ if (z->free_pages > min + z->pages_min) {
page = rmqueue(z, order);
if (page)
return page;
Regards,
Juanma
--
/jm
next reply other threads:[~2002-09-17 21:40 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-09-17 21:48 Juan M. de la Torre [this message]
2002-09-17 22:02 ` Possible bug in __alloc_pages() ? Martin J. Bligh
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=20020917214804.GA891@apocalipsis \
--to=jmtorre@gmx.net \
--cc=linux-kernel@vger.kernel.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