RE: [PATCH 11/12] percpu: convert chunk hints to be based on pcpu_block_md

From: Peng Fan
Date: Sun Mar 03 2019 - 03:19:06 EST

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> -----Original Message-----
> From: owner-linux-mm@xxxxxxxxx [mailto:owner-linux-mm@xxxxxxxxx] On
> Behalf Of Dennis Zhou
> Sent: 2019年2月28日 10:19
> To: Dennis Zhou <dennis@xxxxxxxxxx>; Tejun Heo <tj@xxxxxxxxxx>; Christoph
> Lameter <cl@xxxxxxxxx>
> Cc: Vlad Buslov <vladbu@xxxxxxxxxxxx>; kernel-team@xxxxxx;
> linux-mm@xxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: [PATCH 11/12] percpu: convert chunk hints to be based on
> pcpu_block_md
>
> As mentioned in the last patch, a chunk's hints are no different than a block
> just responsible for more bits. This converts chunk level hints to use a
> pcpu_block_md to maintain them. This lets us reuse the same hint helper
> functions as a block. The left_free and right_free are unused by the chunk's
> pcpu_block_md.
>
> Signed-off-by: Dennis Zhou <dennis@xxxxxxxxxx>
> ---
> mm/percpu-internal.h | 5 +-
> mm/percpu-stats.c | 5 +-
> mm/percpu.c | 120 +++++++++++++++++++------------------------
> 3 files changed, 57 insertions(+), 73 deletions(-)
>
> diff --git a/mm/percpu-internal.h b/mm/percpu-internal.h index
> 119bd1119aa7..0468ba500bd4 100644
> --- a/mm/percpu-internal.h
> +++ b/mm/percpu-internal.h
> @@ -39,9 +39,7 @@ struct pcpu_chunk {
>
> struct list_head list; /* linked to pcpu_slot lists */
> int free_bytes; /* free bytes in the chunk */
> - int contig_bits; /* max contiguous size hint */
> - int contig_bits_start; /* contig_bits starting
> - offset */
> + struct pcpu_block_md chunk_md;
> void *base_addr; /* base address of this chunk */
>
> unsigned long *alloc_map; /* allocation map */
> @@ -49,7 +47,6 @@ struct pcpu_chunk {
> struct pcpu_block_md *md_blocks; /* metadata blocks */
>
> void *data; /* chunk data */
> - int first_bit; /* no free below this */
> bool immutable; /* no [de]population allowed */
> int start_offset; /* the overlap with the previous
> region to have a page aligned
> diff --git a/mm/percpu-stats.c b/mm/percpu-stats.c index
> b5fdd43b60c9..ef5034a0464e 100644
> --- a/mm/percpu-stats.c
> +++ b/mm/percpu-stats.c
> @@ -53,6 +53,7 @@ static int find_max_nr_alloc(void) static void
> chunk_map_stats(struct seq_file *m, struct pcpu_chunk *chunk,
> int *buffer)
> {
> + struct pcpu_block_md *chunk_md = &chunk->chunk_md;
> int i, last_alloc, as_len, start, end;
> int *alloc_sizes, *p;
> /* statistics */
> @@ -121,9 +122,9 @@ static void chunk_map_stats(struct seq_file *m,
> struct pcpu_chunk *chunk,
> P("nr_alloc", chunk->nr_alloc);
> P("max_alloc_size", chunk->max_alloc_size);
> P("empty_pop_pages", chunk->nr_empty_pop_pages);
> - P("first_bit", chunk->first_bit);
> + P("first_bit", chunk_md->first_free);
> P("free_bytes", chunk->free_bytes);
> - P("contig_bytes", chunk->contig_bits * PCPU_MIN_ALLOC_SIZE);
> + P("contig_bytes", chunk_md->contig_hint * PCPU_MIN_ALLOC_SIZE);
> P("sum_frag", sum_frag);
> P("max_frag", max_frag);
> P("cur_min_alloc", cur_min_alloc);
> diff --git a/mm/percpu.c b/mm/percpu.c
> index 7cdf14c242de..197479f2c489 100644
> --- a/mm/percpu.c
> +++ b/mm/percpu.c
> @@ -233,10 +233,13 @@ static int pcpu_size_to_slot(int size)
>
> static int pcpu_chunk_slot(const struct pcpu_chunk *chunk) {
> - if (chunk->free_bytes < PCPU_MIN_ALLOC_SIZE || chunk->contig_bits
> == 0)
> + const struct pcpu_block_md *chunk_md = &chunk->chunk_md;
> +
> + if (chunk->free_bytes < PCPU_MIN_ALLOC_SIZE ||
> + chunk_md->contig_hint == 0)
> return 0;
>
> - return pcpu_size_to_slot(chunk->contig_bits * PCPU_MIN_ALLOC_SIZE);
> + return pcpu_size_to_slot(chunk_md->contig_hint *
> PCPU_MIN_ALLOC_SIZE);
> }
>
> /* set the pointer to a chunk in a page struct */ @@ -592,54 +595,6 @@
> static inline bool pcpu_region_overlap(int a, int b, int x, int y)
> return false;
> }
>
> -/**
> - * pcpu_chunk_update - updates the chunk metadata given a free area
> - * @chunk: chunk of interest
> - * @bit_off: chunk offset
> - * @bits: size of free area
> - *
> - * This updates the chunk's contig hint and starting offset given a free area.
> - * Choose the best starting offset if the contig hint is equal.
> - */
> -static void pcpu_chunk_update(struct pcpu_chunk *chunk, int bit_off, int bits)
> -{
> - if (bits > chunk->contig_bits) {
> - chunk->contig_bits_start = bit_off;
> - chunk->contig_bits = bits;
> - } else if (bits == chunk->contig_bits && chunk->contig_bits_start &&
> - (!bit_off ||
> - __ffs(bit_off) > __ffs(chunk->contig_bits_start))) {
> - /* use the start with the best alignment */
> - chunk->contig_bits_start = bit_off;
> - }
> -}
> -
> -/**
> - * pcpu_chunk_refresh_hint - updates metadata about a chunk
> - * @chunk: chunk of interest
> - *
> - * Iterates over the metadata blocks to find the largest contig area.
> - * It also counts the populated pages and uses the delta to update the
> - * global count.
> - *
> - * Updates:
> - * chunk->contig_bits
> - * chunk->contig_bits_start
> - */
> -static void pcpu_chunk_refresh_hint(struct pcpu_chunk *chunk) -{
> - int bit_off, bits;
> -
> - /* clear metadata */
> - chunk->contig_bits = 0;
> -
> - bit_off = chunk->first_bit;
> - bits = 0;
> - pcpu_for_each_md_free_region(chunk, bit_off, bits) {
> - pcpu_chunk_update(chunk, bit_off, bits);
> - }
> -}
> -
> /**
> * pcpu_block_update - updates a block given a free area
> * @block: block of interest
> @@ -753,6 +708,29 @@ static void pcpu_block_update_scan(struct
> pcpu_chunk *chunk, int bit_off,
> pcpu_block_update(block, s_off, e_off); }
>
> +/**
> + * pcpu_chunk_refresh_hint - updates metadata about a chunk
> + * @chunk: chunk of interest
> + *
> + * Iterates over the metadata blocks to find the largest contig area.
> + * It also counts the populated pages and uses the delta to update the
> + * global count.
> + */
> +static void pcpu_chunk_refresh_hint(struct pcpu_chunk *chunk) {
> + struct pcpu_block_md *chunk_md = &chunk->chunk_md;
> + int bit_off, bits;
> +
> + /* clear metadata */
> + chunk_md->contig_hint = 0;
> +
> + bit_off = chunk_md->first_free;
> + bits = 0;
> + pcpu_for_each_md_free_region(chunk, bit_off, bits) {
> + pcpu_block_update(chunk_md, bit_off, bit_off + bits);
> + }
> +}
> +
> /**
> * pcpu_block_refresh_hint
> * @chunk: chunk of interest
> @@ -800,6 +778,7 @@ static void pcpu_block_refresh_hint(struct
> pcpu_chunk *chunk, int index) static void
> pcpu_block_update_hint_alloc(struct pcpu_chunk *chunk, int bit_off,
> int bits)
> {
> + struct pcpu_block_md *chunk_md = &chunk->chunk_md;
> int nr_empty_pages = 0;
> struct pcpu_block_md *s_block, *e_block, *block;
> int s_index, e_index; /* block indexes of the freed allocation */
> @@ -910,8 +889,9 @@ static void pcpu_block_update_hint_alloc(struct
> pcpu_chunk *chunk, int bit_off,
> * contig hint is broken. Otherwise, it means a smaller space
> * was used and therefore the chunk contig hint is still correct.
> */
> - if (pcpu_region_overlap(chunk->contig_bits_start,
> - chunk->contig_bits_start + chunk->contig_bits,
> + if (pcpu_region_overlap(chunk_md->contig_hint_start,
> + chunk_md->contig_hint_start +
> + chunk_md->contig_hint,
> bit_off,
> bit_off + bits))
> pcpu_chunk_refresh_hint(chunk);
> @@ -930,9 +910,10 @@ static void pcpu_block_update_hint_alloc(struct
> pcpu_chunk *chunk, int bit_off,
> *
> * A chunk update is triggered if a page becomes free, a block becomes free,
> * or the free spans across blocks. This tradeoff is to minimize iterating
> - * over the block metadata to update chunk->contig_bits.
> chunk->contig_bits
> - * may be off by up to a page, but it will never be more than the available
> - * space. If the contig hint is contained in one block, it will be accurate.
> + * over the block metadata to update chunk_md->contig_hint.
> + * chunk_md->contig_hint may be off by up to a page, but it will never
> + be more
> + * than the available space. If the contig hint is contained in one
> + block, it
> + * will be accurate.
> */
> static void pcpu_block_update_hint_free(struct pcpu_chunk *chunk, int
> bit_off,
> int bits)
> @@ -1026,8 +1007,9 @@ static void pcpu_block_update_hint_free(struct
> pcpu_chunk *chunk, int bit_off,
> if (((end - start) >= PCPU_BITMAP_BLOCK_BITS) || s_index != e_index)
> pcpu_chunk_refresh_hint(chunk);
> else
> - pcpu_chunk_update(chunk, pcpu_block_off_to_off(s_index, start),
> - end - start);
> + pcpu_block_update(&chunk->chunk_md,
> + pcpu_block_off_to_off(s_index, start),
> + end);
> }
>
> /**
> @@ -1082,6 +1064,7 @@ static bool pcpu_is_populated(struct pcpu_chunk
> *chunk, int bit_off, int bits, static int pcpu_find_block_fit(struct pcpu_chunk
> *chunk, int alloc_bits,
> size_t align, bool pop_only)
> {
> + struct pcpu_block_md *chunk_md = &chunk->chunk_md;
> int bit_off, bits, next_off;
>
> /*
> @@ -1090,12 +1073,12 @@ static int pcpu_find_block_fit(struct pcpu_chunk
> *chunk, int alloc_bits,
> * cannot fit in the global hint, there is memory pressure and creating
> * a new chunk would happen soon.
> */
> - bit_off = ALIGN(chunk->contig_bits_start, align) -
> - chunk->contig_bits_start;
> - if (bit_off + alloc_bits > chunk->contig_bits)
> + bit_off = ALIGN(chunk_md->contig_hint_start, align) -
> + chunk_md->contig_hint_start;
> + if (bit_off + alloc_bits > chunk_md->contig_hint)
> return -1;
>
> - bit_off = chunk->first_bit;
> + bit_off = chunk_md->first_free;
> bits = 0;
> pcpu_for_each_fit_region(chunk, alloc_bits, align, bit_off, bits) {
> if (!pop_only || pcpu_is_populated(chunk, bit_off, bits, @@ -1190,6
> +1173,7 @@ static unsigned long pcpu_find_zero_area(unsigned long *map,
> static int pcpu_alloc_area(struct pcpu_chunk *chunk, int alloc_bits,
> size_t align, int start)
> {
> + struct pcpu_block_md *chunk_md = &chunk->chunk_md;
> size_t align_mask = (align) ? (align - 1) : 0;
> unsigned long area_off = 0, area_bits = 0;
> int bit_off, end, oslot;
> @@ -1222,8 +1206,8 @@ static int pcpu_alloc_area(struct pcpu_chunk
> *chunk, int alloc_bits,
> chunk->free_bytes -= alloc_bits * PCPU_MIN_ALLOC_SIZE;
>
> /* update first free bit */
> - if (bit_off == chunk->first_bit)
> - chunk->first_bit = find_next_zero_bit(
> + if (bit_off == chunk_md->first_free)
> + chunk_md->first_free = find_next_zero_bit(
> chunk->alloc_map,
> pcpu_chunk_map_bits(chunk),
> bit_off + alloc_bits);
> @@ -1245,6 +1229,7 @@ static int pcpu_alloc_area(struct pcpu_chunk
> *chunk, int alloc_bits,
> */
> static void pcpu_free_area(struct pcpu_chunk *chunk, int off) {
> + struct pcpu_block_md *chunk_md = &chunk->chunk_md;
> int bit_off, bits, end, oslot;
>
> lockdep_assert_held(&pcpu_lock);
> @@ -1264,7 +1249,7 @@ static void pcpu_free_area(struct pcpu_chunk
> *chunk, int off)
> chunk->free_bytes += bits * PCPU_MIN_ALLOC_SIZE;
>
> /* update first free bit */
> - chunk->first_bit = min(chunk->first_bit, bit_off);
> + chunk_md->first_free = min(chunk_md->first_free, bit_off);
>
> pcpu_block_update_hint_free(chunk, bit_off, bits);
>
> @@ -1285,6 +1270,9 @@ static void pcpu_init_md_blocks(struct pcpu_chunk
> *chunk) {
> struct pcpu_block_md *md_block;
>
> + /* init the chunk's block */
> + pcpu_init_md_block(&chunk->chunk_md,
> pcpu_chunk_map_bits(chunk));
> +
> for (md_block = chunk->md_blocks;
> md_block != chunk->md_blocks + pcpu_chunk_nr_blocks(chunk);
> md_block++)
> @@ -1352,7 +1340,6 @@ static struct pcpu_chunk * __init
> pcpu_alloc_first_chunk(unsigned long tmp_addr,
> chunk->nr_populated = chunk->nr_pages;
> chunk->nr_empty_pop_pages = chunk->nr_pages;
>
> - chunk->contig_bits = map_size / PCPU_MIN_ALLOC_SIZE;
> chunk->free_bytes = map_size;
>
> if (chunk->start_offset) {
> @@ -1362,7 +1349,7 @@ static struct pcpu_chunk * __init
> pcpu_alloc_first_chunk(unsigned long tmp_addr,
> set_bit(0, chunk->bound_map);
> set_bit(offset_bits, chunk->bound_map);
>
> - chunk->first_bit = offset_bits;
> + chunk->chunk_md.first_free = offset_bits;
>
> pcpu_block_update_hint_alloc(chunk, 0, offset_bits);
> }
> @@ -1415,7 +1402,6 @@ static struct pcpu_chunk *pcpu_alloc_chunk(gfp_t
> gfp)
> pcpu_init_md_blocks(chunk);
>
> /* init metadata */
> - chunk->contig_bits = region_bits;
> chunk->free_bytes = chunk->nr_pages * PAGE_SIZE;
>
> return chunk;

Reviewed-by: Peng Fan <peng.fan@xxxxxxx>

Nitpick, how about name a function __pcpu_md_update,
and let pcpu_chunk_update and pcpu_block_update to
call __pcpu_md_update. If you prefer, I could submit
a patch.

Thanks,
Peng.

> --
> 2.17.1

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