| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <CACSyD1N5--8DSaJrf0JB-n+OsUFvuuQNau5kCmkP8eo2wyN4wQ@mail.gmail.com>
Date: Thu, 10 Apr 2025 12:50:45 +0800
From: Zhongkun He <hezhongkun.hzk@...edance.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: hannes@...xchg.org, mhocko@...e.com, yosry.ahmed@...ux.dev,
muchun.song@...ux.dev, yuzhao@...gle.com, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [External] Re: [PATCH V3 2/3] mm: add max swappiness arg to
lru_gen for anonymous memory only
On Thu, Apr 10, 2025 at 10:10 AM Andrew Morton
<akpm@...ux-foundation.org> wrote:
>
> On Wed, 9 Apr 2025 15:06:19 +0800 Zhongkun He <hezhongkun.hzk@...edance.com> wrote:
>
> > The MGLRU
>
> paging yuzhao?
I have cc yuzhao and look forward to the relay.
>
> > already supports reclaiming only from anonymous memory
> > via the /sys/kernel/debug/lru_gen interface. Now, memory.reclaim
> > also supports the swappiness=max parameter to enable reclaiming
> > solely from anonymous memory. To unify the semantics of proactive
> > reclaiming from anonymous folios, the max parameter is introduced.
> >
> > Additionally, the use of SWAPPINESS_ANON_ONLY in place of
> > 'MAX_SWAPPINESS + 1' improves code clarity and makes the intention
> > more explicit.
> >
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -2697,8 +2697,11 @@ static bool should_clear_pmd_young(void)
> > READ_ONCE((lruvec)->lrugen.min_seq[LRU_GEN_FILE]), \
> > }
> >
> > +#define max_evictable_type(swappiness) \
> > + ((swappiness) != SWAPPINESS_ANON_ONLY)
> > +
> > #define evictable_min_seq(min_seq, swappiness) \
> > - min((min_seq)[!(swappiness)], (min_seq)[(swappiness) <= MAX_SWAPPINESS])
> > + min((min_seq)[!(swappiness)], (min_seq)[max_evictable_type(swappiness)])
>
> Why oh why did we implement these in cpp?
Just want to make the code more clear. Maybe we should do more like this
/* The range of swappiness is [0,1-200,201], 0 means file type only;
* 1-200 anon and file type; 201 anon type only
*/
#define max_type(swappiness) ((swappiness) != SWAPPINESS_ANON_ONLY)
#define min_type(swappiness) !(swappiness)
#define evictable_min_seq(min_seq, swappiness) \
min((min_seq)[min_type(swappiness)], (min_seq)[max_type(swappiness)])
#define for_each_evictable_type(type, swappiness) \
- for ((type) = !(swappiness); (type) <= ((swappiness) <=
MAX_SWAPPINESS); (type)++)
+ for ((type) = min_type(swappiness) ; (type) <=
max_type(swappiness); (type)++)
>
> >
> > @@ -3857,7 +3860,7 @@ static bool inc_min_seq(struct lruvec *lruvec, int type, int swappiness)
> > int hist = lru_hist_from_seq(lrugen->min_seq[type]);
> > int new_gen, old_gen = lru_gen_from_seq(lrugen->min_seq[type]);
> >
> > - if (type ? swappiness > MAX_SWAPPINESS : !swappiness)
> > + if (type ? (swappiness == SWAPPINESS_ANON_ONLY) : !swappiness)
>
> This expression makes my brain bleed.
>
> if (type) {
> if (swappiness == SWAPPINESS_ANON_ONLY) {
> /*
> * Nice comment explaining why we're doing this
> */
> goto done;;
> }
> } else {
> if (!swappiness) {
> /*
> * Nice comment explaining why we're doing this
> */
> goto done;
> }
> }
>
> or
>
> if (type && (swappiness == SWAPPINESS_ANON_ONLY)) {
> /*
> * Nice comment explaining why we're doing this
> */
> goto done;
> }
>
> if (!type && !swappiness) {
> /*
> * Nice comment explaining why we're doing this
> */
> goto done;
> }
>
> It's much more verbose, but it has the huge advantage that it creates
> locations where we can add comments which tell readers what's going on.
> Which is pretty important, no?
>
Yes, I agree. Will do, thanks.
> > goto done;
> >
> > /* prevent cold/hot inversion if the type is evictable */
> > @@ -5523,7 +5526,7 @@ static int run_cmd(char cmd, int memcg_id, int nid, unsigned long seq,
> >
> > if (swappiness < MIN_SWAPPINESS)
> > swappiness = get_swappiness(lruvec, sc);
> > - else if (swappiness > MAX_SWAPPINESS + 1)
> > + else if (swappiness > SWAPPINESS_ANON_ONLY)
> > goto done;
> >
> > switch (cmd) {
> > @@ -5580,7 +5583,7 @@ static ssize_t lru_gen_seq_write(struct file *file, const char __user *src,
> > while ((cur = strsep(&next, ",;\n"))) {
> > int n;
> > int end;
> > - char cmd;
> > + char cmd, swap_string[5];
> > unsigned int memcg_id;
> > unsigned int nid;
> > unsigned long seq;
> > @@ -5591,13 +5594,22 @@ static ssize_t lru_gen_seq_write(struct file *file, const char __user *src,
> > if (!*cur)
> > continue;
> >
> > - n = sscanf(cur, "%c %u %u %lu %n %u %n %lu %n", &cmd, &memcg_id, &nid,
> > - &seq, &end, &swappiness, &end, &opt, &end);
> > + n = sscanf(cur, "%c %u %u %lu %n %4s %n %lu %n", &cmd, &memcg_id, &nid,
> > + &seq, &end, swap_string, &end, &opt, &end);
>
> Permits userspace to easily overrun swap_string[]. OK, it's root-only,
> but still, why permit this?
>
IICC, the arg in sscanf is %4s meaning the length of the string will
not be allowed to overrun
the swap_string, thanks.
> > if (n < 4 || cur[end]) {
> > err = -EINVAL;
> > break;
> > }
> >
> > + /* set by userspace for anonymous memory only */
> > + if (!strncmp("max", swap_string, sizeof("max"))) {
>
> Can sscanf() give us a non null-terminated string?
>
No, the sscanf will add '\0' to the end, so the maximum number of
input characters is 4,
and the length of swap_string is 5, with one character reserved for
the null terminator '\0'
for sscanf.
Thanks for your time.
> > + swappiness = SWAPPINESS_ANON_ONLY;
> > + } else {
> > + err = kstrtouint(swap_string, 0, &swappiness);
> > + if (err)
> > + break;
> > + }
> > +
> > err = run_cmd(cmd, memcg_id, nid, seq, &sc, swappiness, opt);
> > if (err)
> > break;
>
Powered by blists - more mailing lists