> -----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 12/12] percpu: use chunk scan_hint to skip some scanning > > Just like blocks, chunks now maintain a scan_hint. This can be used to skip > some scanning by promoting the scan_hint to be the contig_hint. > The chunk's scan_hint is primarily updated on the backside and relies on full > scanning when a block becomes free or the free region spans across blocks. > > Signed-off-by: Dennis Zhou <dennis@xxxxxxxxxx> > --- > mm/percpu.c | 36 +++++++++++++++++++++++++++--------- > 1 file changed, 27 insertions(+), 9 deletions(-) > > diff --git a/mm/percpu.c b/mm/percpu.c > index 197479f2c489..40d49d7fb286 100644 > --- a/mm/percpu.c > +++ b/mm/percpu.c > @@ -711,20 +711,31 @@ static void pcpu_block_update_scan(struct > pcpu_chunk *chunk, int bit_off, > /** > * pcpu_chunk_refresh_hint - updates metadata about a chunk > * @chunk: chunk of interest > + * @full_scan: if we should scan from the beginning > * > * 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. > + * A full scan can be avoided on the allocation path as this is > + triggered > + * if we broke the contig_hint. In doing so, the scan_hint will be > + before > + * the contig_hint or after if the scan_hint == contig_hint. This > + cannot > + * be prevented on freeing as we want to find the largest area possibly > + * spanning blocks. > */ > -static void pcpu_chunk_refresh_hint(struct pcpu_chunk *chunk) > +static void pcpu_chunk_refresh_hint(struct pcpu_chunk *chunk, bool > +full_scan) > { > struct pcpu_block_md *chunk_md = &chunk->chunk_md; > int bit_off, bits; > > - /* clear metadata */ > - chunk_md->contig_hint = 0; > + /* promote scan_hint to contig_hint */ > + if (!full_scan && chunk_md->scan_hint) { > + bit_off = chunk_md->scan_hint_start + chunk_md->scan_hint; > + chunk_md->contig_hint_start = chunk_md->scan_hint_start; > + chunk_md->contig_hint = chunk_md->scan_hint; > + chunk_md->scan_hint = 0; > + } else { > + bit_off = chunk_md->first_free; > + 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); @@ -884,6 > +895,13 @@ static void pcpu_block_update_hint_alloc(struct pcpu_chunk > *chunk, int bit_off, > if (nr_empty_pages) > pcpu_update_empty_pages(chunk, -1 * nr_empty_pages); > > + if (pcpu_region_overlap(chunk_md->scan_hint_start, > + chunk_md->scan_hint_start + > + chunk_md->scan_hint, > + bit_off, > + bit_off + bits)) > + chunk_md->scan_hint = 0; > + > /* > * The only time a full chunk scan is required is if the chunk > * contig hint is broken. Otherwise, it means a smaller space @@ > -894,7 +912,7 @@ static void pcpu_block_update_hint_alloc(struct > pcpu_chunk *chunk, int bit_off, > chunk_md->contig_hint, > bit_off, > bit_off + bits)) > - pcpu_chunk_refresh_hint(chunk); > + pcpu_chunk_refresh_hint(chunk, false); > } > > /** > @@ -1005,7 +1023,7 @@ static void pcpu_block_update_hint_free(struct > pcpu_chunk *chunk, int bit_off, > * the else condition below. > */ > if (((end - start) >= PCPU_BITMAP_BLOCK_BITS) || s_index != e_index) > - pcpu_chunk_refresh_hint(chunk); > + pcpu_chunk_refresh_hint(chunk, true); > else > pcpu_block_update(&chunk->chunk_md, > pcpu_block_off_to_off(s_index, start), @@ -1078,7 > +1096,7 @@ static int pcpu_find_block_fit(struct pcpu_chunk *chunk, int > alloc_bits, > if (bit_off + alloc_bits > chunk_md->contig_hint) > return -1; > > - bit_off = chunk_md->first_free; > + bit_off = pcpu_next_hint(chunk_md, alloc_bits); > bits = 0; > pcpu_for_each_fit_region(chunk, alloc_bits, align, bit_off, bits) { > if (!pop_only || pcpu_is_populated(chunk, bit_off, bits, Reviewed-by: Peng Fan <peng.fan@xxxxxxx> > -- > 2.17.1
