| Message ID | b3af3747daefa00177b48f4666780da58177f7c0.1744169302.git.hezhongkun.hzk@bytedance.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | add max arg to swappiness in memory.reclaim and lru_gen | expand |
On Wed, 9 Apr 2025 15:06:19 +0800 Zhongkun He <hezhongkun.hzk@bytedance.com> wrote: > The MGLRU paging yuzhao? > 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? > > @@ -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? > 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? > 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? > + 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;
On Thu, Apr 10, 2025 at 10:10 AM Andrew Morton <akpm@linux-foundation.org> wrote: > > On Wed, 9 Apr 2025 15:06:19 +0800 Zhongkun He <hezhongkun.hzk@bytedance.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; >
diff --git a/Documentation/admin-guide/mm/multigen_lru.rst b/Documentation/admin-guide/mm/multigen_lru.rst index 33e068830497..9cb54b4ff5d9 100644 --- a/Documentation/admin-guide/mm/multigen_lru.rst +++ b/Documentation/admin-guide/mm/multigen_lru.rst @@ -151,8 +151,9 @@ generations less than or equal to ``min_gen_nr``. ``min_gen_nr`` should be less than ``max_gen_nr-1``, since ``max_gen_nr`` and ``max_gen_nr-1`` are not fully aged (equivalent to the active list) and therefore cannot be evicted. ``swappiness`` -overrides the default value in ``/proc/sys/vm/swappiness``. -``nr_to_reclaim`` limits the number of pages to evict. +overrides the default value in ``/proc/sys/vm/swappiness`` and the valid +range is [0-200, max], with max being exclusively used for the reclamation +of anonymous memory. ``nr_to_reclaim`` limits the number of pages to evict. A typical use case is that a job scheduler runs this command before it tries to land a new job on a server. If it fails to materialize enough diff --git a/mm/vmscan.c b/mm/vmscan.c index c99a6a48d0bc..18a175752b57 100644 --- 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)]) #define for_each_gen_type_zone(gen, type, zone) \ for ((gen) = 0; (gen) < MAX_NR_GENS; (gen)++) \ @@ -2706,7 +2709,7 @@ static bool should_clear_pmd_young(void) for ((zone) = 0; (zone) < MAX_NR_ZONES; (zone)++) #define for_each_evictable_type(type, swappiness) \ - for ((type) = !(swappiness); (type) <= ((swappiness) <= MAX_SWAPPINESS); (type)++) + for ((type) = !(swappiness); (type) <= max_evictable_type(swappiness); (type)++) #define get_memcg_gen(seq) ((seq) % MEMCG_NR_GENS) #define get_memcg_bin(bin) ((bin) % MEMCG_NR_BINS) @@ -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) 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); if (n < 4 || cur[end]) { err = -EINVAL; break; } + /* set by userspace for anonymous memory only */ + if (!strncmp("max", swap_string, sizeof("max"))) { + 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;
The MGLRU 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. Signed-off-by: Zhongkun He <hezhongkun.hzk@bytedance.com> --- Documentation/admin-guide/mm/multigen_lru.rst | 5 ++-- mm/vmscan.c | 26 ++++++++++++++----- 2 files changed, 22 insertions(+), 9 deletions(-)