Hi Dennis, > -----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 03/12] percpu: introduce helper to determine if two regions > overlap > > While block hints were always accurate, it's possible when spanning across > blocks that we miss updating the chunk's contig_hint. Rather than rely on > correctness of the boundaries of hints, do a full overlap comparison. > > Signed-off-by: Dennis Zhou <dennis@xxxxxxxxxx> > --- > mm/percpu.c | 31 +++++++++++++++++++++++++++---- > 1 file changed, 27 insertions(+), 4 deletions(-) > > diff --git a/mm/percpu.c b/mm/percpu.c > index 69ca51d238b5..b40112b2fc59 100644 > --- a/mm/percpu.c > +++ b/mm/percpu.c > @@ -546,6 +546,24 @@ static inline int pcpu_cnt_pop_pages(struct > pcpu_chunk *chunk, int bit_off, > bitmap_weight(chunk->populated, page_start); } > > +/* > + * pcpu_region_overlap - determines if two regions overlap > + * @a: start of first region, inclusive > + * @b: end of first region, exclusive > + * @x: start of second region, inclusive > + * @y: end of second region, exclusive > + * > + * This is used to determine if the hint region [a, b) overlaps with > +the > + * allocated region [x, y). > + */ > +static inline bool pcpu_region_overlap(int a, int b, int x, int y) { > + if ((x >= a && x < b) || (y > a && y <= b) || > + (x <= a && y >= b)) I think this could be simplified: (a < y) && (x < b) could be used to do overlap check. Regards, Peng. > + return true; > + return false; > +} > + > /** > * pcpu_chunk_update - updates the chunk metadata given a free area > * @chunk: chunk of interest > @@ -710,8 +728,11 @@ static void pcpu_block_update_hint_alloc(struct > pcpu_chunk *chunk, int bit_off, > PCPU_BITMAP_BLOCK_BITS, > s_off + bits); > > - if (s_off >= s_block->contig_hint_start && > - s_off < s_block->contig_hint_start + s_block->contig_hint) { > + if (pcpu_region_overlap(s_block->contig_hint_start, > + s_block->contig_hint_start + > + s_block->contig_hint, > + s_off, > + s_off + bits)) { > /* block contig hint is broken - scan to fix it */ > pcpu_block_refresh_hint(chunk, s_index); > } else { > @@ -764,8 +785,10 @@ 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 (bit_off >= chunk->contig_bits_start && > - bit_off < chunk->contig_bits_start + chunk->contig_bits) > + if (pcpu_region_overlap(chunk->contig_bits_start, > + chunk->contig_bits_start + chunk->contig_bits, > + bit_off, > + bit_off + bits)) > pcpu_chunk_refresh_hint(chunk); > } > > -- > 2.17.1
