On Sat, Mar 02, 2019 at 01:37:37PM +0000, Peng Fan wrote: > 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. > I'll change it to be the negative. Thanks, Dennis > > > + 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 >
