On Mon, Oct 24, 2022 at 04:14:31PM +0800, Baoquan He wrote: > When allocating an area from a chunk, pcpu_block_update_hint_alloc() > is called to update chunk metadata, including chunk's and global > nr_empty_pop_pages. However, if the allocation is not atomic, some > blocks may not be populated with pages yet, while we still account it > here. The number of pages will be subtracted with pcpu_chunk_populated() > when populating pages. > > Adding code comment to make that more understandable. > > Signed-off-by: Baoquan He <bhe@xxxxxxxxxx> > --- > mm/percpu.c | 14 +++++++++++--- > 1 file changed, 11 insertions(+), 3 deletions(-) > > diff --git a/mm/percpu.c b/mm/percpu.c > index a8121302a79c..09e407338573 100644 > --- a/mm/percpu.c > +++ b/mm/percpu.c > @@ -831,13 +831,15 @@ static void pcpu_block_update_hint_alloc(struct pcpu_chunk *chunk, int bit_off, > > /* > * Update s_block. > - * block->first_free must be updated if the allocation takes its place. > - * If the allocation breaks the contig_hint, a scan is required to > - * restore this hint. > */ > if (s_block->contig_hint == PCPU_BITMAP_BLOCK_BITS) > nr_empty_pages++; > > + /* > + * block->first_free must be updated if the allocation takes its place. > + * If the allocation breaks the contig_hint, a scan is required to > + * restore this hint. > + */ > if (s_off == s_block->first_free) > s_block->first_free = find_next_zero_bit( > pcpu_index_alloc_map(chunk, s_index), > @@ -912,6 +914,12 @@ static void pcpu_block_update_hint_alloc(struct pcpu_chunk *chunk, int bit_off, > } > } > > + /* > + * If the allocation is not atomic, some blocks may not > + * be populated with pages, while we account it here. > + * The number of pages will be subtracted with > + * pcpu_chunk_populated() when populating pages. > + */ > if (nr_empty_pages) > pcpu_update_empty_pages(chunk, -nr_empty_pages); > > -- > 2.34.1 > Heh, that's a little more subtle than I remember it being. Acked-by: Dennis Zhou <dennis@xxxxxxxxxx> Thanks, Dennis
