| Message ID | 20190228021839.55779-8-dennis@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | introduce percpu block scan_hint | expand |
Hi Dennis > -----Original Message----- > From: owner-linux-mm@kvack.org [mailto:owner-linux-mm@kvack.org] On > Behalf Of Dennis Zhou > Sent: 2019年2月28日 10:19 > To: Dennis Zhou <dennis@kernel.org>; Tejun Heo <tj@kernel.org>; Christoph > Lameter <cl@linux.com> > Cc: Vlad Buslov <vladbu@mellanox.com>; kernel-team@fb.com; > linux-mm@kvack.org; linux-kernel@vger.kernel.org > Subject: [PATCH 07/12] percpu: add block level scan_hint > > Fragmentation can cause both blocks and chunks to have an early first_firee > bit available, but only able to satisfy allocations much later on. This patch > introduces a scan_hint to help mitigate some unnecessary scanning. > > The scan_hint remembers the largest area prior to the contig_hint. If the > contig_hint == scan_hint, then scan_hint_start > contig_hint_start. > This is necessary for scan_hint discovery when refreshing a block. > > Signed-off-by: Dennis Zhou <dennis@kernel.org> > --- > mm/percpu-internal.h | 9 ++++ > mm/percpu.c | 101 > ++++++++++++++++++++++++++++++++++++++++--- > 2 files changed, 103 insertions(+), 7 deletions(-) > > diff --git a/mm/percpu-internal.h b/mm/percpu-internal.h index > b1739dc06b73..ec58b244545d 100644 > --- a/mm/percpu-internal.h > +++ b/mm/percpu-internal.h > @@ -9,8 +9,17 @@ > * pcpu_block_md is the metadata block struct. > * Each chunk's bitmap is split into a number of full blocks. > * All units are in terms of bits. > + * > + * The scan hint is the largest known contiguous area before the contig hint. > + * It is not necessarily the actual largest contig hint though. There > + is an > + * invariant that the scan_hint_start > contig_hint_start iff > + * scan_hint == contig_hint. This is necessary because when scanning > + forward, > + * we don't know if a new contig hint would be better than the current one. > */ > struct pcpu_block_md { > + int scan_hint; /* scan hint for block */ > + int scan_hint_start; /* block relative starting > + position of the scan hint */ > int contig_hint; /* contig hint for block */ > int contig_hint_start; /* block relative starting > position of the contig hint */ diff --git > a/mm/percpu.c b/mm/percpu.c index 967c9cc3a928..df1aacf58ac8 100644 > --- a/mm/percpu.c > +++ b/mm/percpu.c > @@ -320,6 +320,34 @@ static unsigned long pcpu_block_off_to_off(int index, > int off) > return index * PCPU_BITMAP_BLOCK_BITS + off; } > > +/* > + * pcpu_next_hint - determine which hint to use > + * @block: block of interest > + * @alloc_bits: size of allocation > + * > + * This determines if we should scan based on the scan_hint or first_free. > + * In general, we want to scan from first_free to fulfill allocations > +by > + * first fit. However, if we know a scan_hint at position > +scan_hint_start > + * cannot fulfill an allocation, we can begin scanning from there > +knowing > + * the contig_hint will be our fallback. > + */ > +static int pcpu_next_hint(struct pcpu_block_md *block, int alloc_bits) > +{ > + /* > + * The three conditions below determine if we can skip past the > + * scan_hint. First, does the scan hint exist. Second, is the > + * contig_hint after the scan_hint (possibly not true iff > + * contig_hint == scan_hint). Third, is the allocation request > + * larger than the scan_hint. > + */ > + if (block->scan_hint && > + block->contig_hint_start > block->scan_hint_start && > + alloc_bits > block->scan_hint) > + return block->scan_hint_start + block->scan_hint; > + > + return block->first_free; > +} > + > /** > * pcpu_next_md_free_region - finds the next hint free area > * @chunk: chunk of interest > @@ -415,9 +443,11 @@ static void pcpu_next_fit_region(struct pcpu_chunk > *chunk, int alloc_bits, > if (block->contig_hint && > block->contig_hint_start >= block_off && > block->contig_hint >= *bits + alloc_bits) { > + int start = pcpu_next_hint(block, alloc_bits); > + > *bits += alloc_bits + block->contig_hint_start - > - block->first_free; > - *bit_off = pcpu_block_off_to_off(i, block->first_free); > + start; This might not relevant to this patch. Not sure it is intended or not. For `alloc_bits + block->contig_hink_start - [block->first_free or start]` If the reason is to let pcpu_is_populated return a proper next_off when pcpu_is_populated fail, it makes sense. If not, why not just use *bits += alloc_bits. > + *bit_off = pcpu_block_off_to_off(i, start); > return; > } > /* reset to satisfy the second predicate above */ @@ -632,12 > +662,57 @@ static void pcpu_block_update(struct pcpu_block_md *block, int > start, int end) > block->right_free = contig; > > if (contig > block->contig_hint) { > + /* promote the old contig_hint to be the new scan_hint */ > + if (start > block->contig_hint_start) { > + if (block->contig_hint > block->scan_hint) { > + block->scan_hint_start = > + block->contig_hint_start; > + block->scan_hint = block->contig_hint; > + } else if (start < block->scan_hint_start) { > + /* > + * The old contig_hint == scan_hint. But, the > + * new contig is larger so hold the invariant > + * scan_hint_start < contig_hint_start. > + */ > + block->scan_hint = 0; > + } > + } else { > + block->scan_hint = 0; > + } > block->contig_hint_start = start; > block->contig_hint = contig; > - } else if (block->contig_hint_start && contig == block->contig_hint && > - (!start || __ffs(start) > __ffs(block->contig_hint_start))) { > - /* use the start with the best alignment */ > - block->contig_hint_start = start; > + } else if (contig == block->contig_hint) { > + if (block->contig_hint_start && > + (!start || > + __ffs(start) > __ffs(block->contig_hint_start))) { > + /* start has a better alignment so use it */ > + block->contig_hint_start = start; > + if (start < block->scan_hint_start && > + block->contig_hint > block->scan_hint) > + block->scan_hint = 0; > + } else if (start > block->scan_hint_start || > + block->contig_hint > block->scan_hint) { > + /* > + * Knowing contig == contig_hint, update the scan_hint > + * if it is farther than or larger than the current > + * scan_hint. > + */ > + block->scan_hint_start = start; > + block->scan_hint = contig; > + } > + } else { > + /* > + * The region is smaller than the contig_hint. So only update > + * the scan_hint if it is larger than or equal and farther than > + * the current scan_hint. > + */ > + if ((start < block->contig_hint_start && > + (contig > block->scan_hint || > + (contig == block->scan_hint && > + start > block->scan_hint_start)))) { > + block->scan_hint_start = start; > + block->scan_hint = contig; > + } > } > } > > @@ -656,7 +731,7 @@ static void pcpu_block_refresh_hint(struct > pcpu_chunk *chunk, int index) > int rs, re; /* region start, region end */ > > /* clear hints */ > - block->contig_hint = 0; > + block->contig_hint = block->scan_hint = 0; > block->left_free = block->right_free = 0; > > /* iterate over free areas and update the contig hints */ @@ -713,6 > +788,12 @@ static void pcpu_block_update_hint_alloc(struct pcpu_chunk > *chunk, int bit_off, > PCPU_BITMAP_BLOCK_BITS, > s_off + bits); > > + if (pcpu_region_overlap(s_block->scan_hint_start, > + s_block->scan_hint_start + s_block->scan_hint, > + s_off, > + s_off + bits)) > + s_block->scan_hint = 0; > + > if (pcpu_region_overlap(s_block->contig_hint_start, > s_block->contig_hint_start + > s_block->contig_hint, > @@ -749,6 +830,9 @@ static void pcpu_block_update_hint_alloc(struct > pcpu_chunk *chunk, int bit_off, > /* reset the block */ > e_block++; > } else { > + if (e_off > e_block->scan_hint_start) > + e_block->scan_hint = 0; > + > if (e_off > e_block->contig_hint_start) { > /* contig hint is broken - scan to fix it */ > pcpu_block_refresh_hint(chunk, e_index); @@ -763,6 > +847,7 @@ static void pcpu_block_update_hint_alloc(struct pcpu_chunk > *chunk, int bit_off, > /* update in-between md_blocks */ > nr_empty_pages += (e_index - s_index - 1); > for (block = s_block + 1; block < e_block; block++) { > + block->scan_hint = 0; > block->contig_hint = 0; > block->left_free = 0; > block->right_free = 0; > @@ -873,6 +958,7 @@ static void pcpu_block_update_hint_free(struct > pcpu_chunk *chunk, int bit_off, > nr_empty_pages += (e_index - s_index - 1); > for (block = s_block + 1; block < e_block; block++) { > block->first_free = 0; > + block->scan_hint = 0; > block->contig_hint_start = 0; > block->contig_hint = PCPU_BITMAP_BLOCK_BITS; > block->left_free = PCPU_BITMAP_BLOCK_BITS; @@ -1084,6 > +1170,7 @@ static void pcpu_init_md_blocks(struct pcpu_chunk *chunk) > for (md_block = chunk->md_blocks; > md_block != chunk->md_blocks + pcpu_chunk_nr_blocks(chunk); > md_block++) { > + md_block->scan_hint = 0; > md_block->contig_hint = PCPU_BITMAP_BLOCK_BITS; > md_block->left_free = PCPU_BITMAP_BLOCK_BITS; > md_block->right_free = PCPU_BITMAP_BLOCK_BITS; Reviewed-by: Peng Fan <peng.fan@nxp.com> > -- > 2.17.1
On Sun, Mar 03, 2019 at 06:01:42AM +0000, Peng Fan wrote: > Hi Dennis > > > -----Original Message----- > > From: owner-linux-mm@kvack.org [mailto:owner-linux-mm@kvack.org] On > > Behalf Of Dennis Zhou > > Sent: 2019年2月28日 10:19 > > To: Dennis Zhou <dennis@kernel.org>; Tejun Heo <tj@kernel.org>; Christoph > > Lameter <cl@linux.com> > > Cc: Vlad Buslov <vladbu@mellanox.com>; kernel-team@fb.com; > > linux-mm@kvack.org; linux-kernel@vger.kernel.org > > Subject: [PATCH 07/12] percpu: add block level scan_hint > > > > Fragmentation can cause both blocks and chunks to have an early first_firee > > bit available, but only able to satisfy allocations much later on. This patch > > introduces a scan_hint to help mitigate some unnecessary scanning. > > > > The scan_hint remembers the largest area prior to the contig_hint. If the > > contig_hint == scan_hint, then scan_hint_start > contig_hint_start. > > This is necessary for scan_hint discovery when refreshing a block. > > > > Signed-off-by: Dennis Zhou <dennis@kernel.org> > > --- > > mm/percpu-internal.h | 9 ++++ > > mm/percpu.c | 101 > > ++++++++++++++++++++++++++++++++++++++++--- > > 2 files changed, 103 insertions(+), 7 deletions(-) > > > > diff --git a/mm/percpu-internal.h b/mm/percpu-internal.h index > > b1739dc06b73..ec58b244545d 100644 > > --- a/mm/percpu-internal.h > > +++ b/mm/percpu-internal.h > > @@ -9,8 +9,17 @@ > > * pcpu_block_md is the metadata block struct. > > * Each chunk's bitmap is split into a number of full blocks. > > * All units are in terms of bits. > > + * > > + * The scan hint is the largest known contiguous area before the contig hint. > > + * It is not necessarily the actual largest contig hint though. There > > + is an > > + * invariant that the scan_hint_start > contig_hint_start iff > > + * scan_hint == contig_hint. This is necessary because when scanning > > + forward, > > + * we don't know if a new contig hint would be better than the current one. > > */ > > struct pcpu_block_md { > > + int scan_hint; /* scan hint for block */ > > + int scan_hint_start; /* block relative starting > > + position of the scan hint */ > > int contig_hint; /* contig hint for block */ > > int contig_hint_start; /* block relative starting > > position of the contig hint */ diff --git > > a/mm/percpu.c b/mm/percpu.c index 967c9cc3a928..df1aacf58ac8 100644 > > --- a/mm/percpu.c > > +++ b/mm/percpu.c > > @@ -320,6 +320,34 @@ static unsigned long pcpu_block_off_to_off(int index, > > int off) > > return index * PCPU_BITMAP_BLOCK_BITS + off; } > > > > +/* > > + * pcpu_next_hint - determine which hint to use > > + * @block: block of interest > > + * @alloc_bits: size of allocation > > + * > > + * This determines if we should scan based on the scan_hint or first_free. > > + * In general, we want to scan from first_free to fulfill allocations > > +by > > + * first fit. However, if we know a scan_hint at position > > +scan_hint_start > > + * cannot fulfill an allocation, we can begin scanning from there > > +knowing > > + * the contig_hint will be our fallback. > > + */ > > +static int pcpu_next_hint(struct pcpu_block_md *block, int alloc_bits) > > +{ > > + /* > > + * The three conditions below determine if we can skip past the > > + * scan_hint. First, does the scan hint exist. Second, is the > > + * contig_hint after the scan_hint (possibly not true iff > > + * contig_hint == scan_hint). Third, is the allocation request > > + * larger than the scan_hint. > > + */ > > + if (block->scan_hint && > > + block->contig_hint_start > block->scan_hint_start && > > + alloc_bits > block->scan_hint) > > + return block->scan_hint_start + block->scan_hint; > > + > > + return block->first_free; > > +} > > + > > /** > > * pcpu_next_md_free_region - finds the next hint free area > > * @chunk: chunk of interest > > @@ -415,9 +443,11 @@ static void pcpu_next_fit_region(struct pcpu_chunk > > *chunk, int alloc_bits, > > if (block->contig_hint && > > block->contig_hint_start >= block_off && > > block->contig_hint >= *bits + alloc_bits) { > > + int start = pcpu_next_hint(block, alloc_bits); > > + > > *bits += alloc_bits + block->contig_hint_start - > > - block->first_free; > > - *bit_off = pcpu_block_off_to_off(i, block->first_free); > > + start; > > This might not relevant to this patch. > Not sure it is intended or not. > For `alloc_bits + block->contig_hink_start - [block->first_free or start]` > If the reason is to let pcpu_is_populated return a proper next_off when pcpu_is_populated > fail, it makes sense. If not, why not just use *bits += alloc_bits. > This is how the iterator works. Without it, it doesn't. Thanks, Dennis
> -----Original Message----- > From: Dennis Zhou [mailto:dennis@kernel.org] > Sent: 2019年3月4日 4:23 > To: Peng Fan <peng.fan@nxp.com> > Cc: Tejun Heo <tj@kernel.org>; Christoph Lameter <cl@linux.com>; Vlad > Buslov <vladbu@mellanox.com>; kernel-team@fb.com; linux-mm@kvack.org; > linux-kernel@vger.kernel.org > Subject: Re: [PATCH 07/12] percpu: add block level scan_hint > > On Sun, Mar 03, 2019 at 06:01:42AM +0000, Peng Fan wrote: > > Hi Dennis > > > > > -----Original Message----- > > > From: owner-linux-mm@kvack.org [mailto:owner-linux-mm@kvack.org] > On > > > Behalf Of Dennis Zhou > > > Sent: 2019年2月28日 10:19 > > > To: Dennis Zhou <dennis@kernel.org>; Tejun Heo <tj@kernel.org>; > > > Christoph Lameter <cl@linux.com> > > > Cc: Vlad Buslov <vladbu@mellanox.com>; kernel-team@fb.com; > > > linux-mm@kvack.org; linux-kernel@vger.kernel.org > > > Subject: [PATCH 07/12] percpu: add block level scan_hint > > > > > > Fragmentation can cause both blocks and chunks to have an early > > > first_firee bit available, but only able to satisfy allocations much > > > later on. This patch introduces a scan_hint to help mitigate some > unnecessary scanning. > > > > > > The scan_hint remembers the largest area prior to the contig_hint. > > > If the contig_hint == scan_hint, then scan_hint_start > contig_hint_start. > > > This is necessary for scan_hint discovery when refreshing a block. > > > > > > Signed-off-by: Dennis Zhou <dennis@kernel.org> > > > --- > > > mm/percpu-internal.h | 9 ++++ > > > mm/percpu.c | 101 > > > ++++++++++++++++++++++++++++++++++++++++--- > > > 2 files changed, 103 insertions(+), 7 deletions(-) > > > > > > diff --git a/mm/percpu-internal.h b/mm/percpu-internal.h index > > > b1739dc06b73..ec58b244545d 100644 > > > --- a/mm/percpu-internal.h > > > +++ b/mm/percpu-internal.h > > > @@ -9,8 +9,17 @@ > > > * pcpu_block_md is the metadata block struct. > > > * Each chunk's bitmap is split into a number of full blocks. > > > * All units are in terms of bits. > > > + * > > > + * The scan hint is the largest known contiguous area before the contig > hint. > > > + * It is not necessarily the actual largest contig hint though. > > > + There is an > > > + * invariant that the scan_hint_start > contig_hint_start iff > > > + * scan_hint == contig_hint. This is necessary because when > > > + scanning forward, > > > + * we don't know if a new contig hint would be better than the current > one. > > > */ > > > struct pcpu_block_md { > > > + int scan_hint; /* scan hint for block */ > > > + int scan_hint_start; /* block relative starting > > > + position of the scan hint */ > > > int contig_hint; /* contig hint for block > */ > > > int contig_hint_start; /* block relative > starting > > > position of the contig hint */ diff > --git a/mm/percpu.c > > > b/mm/percpu.c index 967c9cc3a928..df1aacf58ac8 100644 > > > --- a/mm/percpu.c > > > +++ b/mm/percpu.c > > > @@ -320,6 +320,34 @@ static unsigned long pcpu_block_off_to_off(int > > > index, int off) > > > return index * PCPU_BITMAP_BLOCK_BITS + off; } > > > > > > +/* > > > + * pcpu_next_hint - determine which hint to use > > > + * @block: block of interest > > > + * @alloc_bits: size of allocation > > > + * > > > + * This determines if we should scan based on the scan_hint or first_free. > > > + * In general, we want to scan from first_free to fulfill > > > +allocations by > > > + * first fit. However, if we know a scan_hint at position > > > +scan_hint_start > > > + * cannot fulfill an allocation, we can begin scanning from there > > > +knowing > > > + * the contig_hint will be our fallback. > > > + */ > > > +static int pcpu_next_hint(struct pcpu_block_md *block, int > > > +alloc_bits) { > > > + /* > > > + * The three conditions below determine if we can skip past the > > > + * scan_hint. First, does the scan hint exist. Second, is the > > > + * contig_hint after the scan_hint (possibly not true iff > > > + * contig_hint == scan_hint). Third, is the allocation request > > > + * larger than the scan_hint. > > > + */ > > > + if (block->scan_hint && > > > + block->contig_hint_start > block->scan_hint_start && > > > + alloc_bits > block->scan_hint) > > > + return block->scan_hint_start + block->scan_hint; > > > + > > > + return block->first_free; > > > +} > > > + > > > /** > > > * pcpu_next_md_free_region - finds the next hint free area > > > * @chunk: chunk of interest > > > @@ -415,9 +443,11 @@ static void pcpu_next_fit_region(struct > > > pcpu_chunk *chunk, int alloc_bits, > > > if (block->contig_hint && > > > block->contig_hint_start >= block_off && > > > block->contig_hint >= *bits + alloc_bits) { > > > + int start = pcpu_next_hint(block, alloc_bits); > > > + > > > *bits += alloc_bits + block->contig_hint_start - > > > - block->first_free; > > > - *bit_off = pcpu_block_off_to_off(i, block->first_free); > > > + start; > > > > This might not relevant to this patch. > > Not sure it is intended or not. > > For `alloc_bits + block->contig_hink_start - [block->first_free or > > start]` If the reason is to let pcpu_is_populated return a proper > > next_off when pcpu_is_populated fail, it makes sense. If not, why not just > use *bits += alloc_bits. > > > > This is how the iterator works. Without it, it doesn't. Oops，I made a mistake, you are right, the iterator needs such logic. Thanks, Peng. > > Thanks, > Dennis
diff --git a/mm/percpu-internal.h b/mm/percpu-internal.h index b1739dc06b73..ec58b244545d 100644 --- a/mm/percpu-internal.h +++ b/mm/percpu-internal.h @@ -9,8 +9,17 @@ * pcpu_block_md is the metadata block struct. * Each chunk's bitmap is split into a number of full blocks. * All units are in terms of bits. + * + * The scan hint is the largest known contiguous area before the contig hint. + * It is not necessarily the actual largest contig hint though. There is an + * invariant that the scan_hint_start > contig_hint_start iff + * scan_hint == contig_hint. This is necessary because when scanning forward, + * we don't know if a new contig hint would be better than the current one. */ struct pcpu_block_md { + int scan_hint; /* scan hint for block */ + int scan_hint_start; /* block relative starting + position of the scan hint */ int contig_hint; /* contig hint for block */ int contig_hint_start; /* block relative starting position of the contig hint */ diff --git a/mm/percpu.c b/mm/percpu.c index 967c9cc3a928..df1aacf58ac8 100644 --- a/mm/percpu.c +++ b/mm/percpu.c @@ -320,6 +320,34 @@ static unsigned long pcpu_block_off_to_off(int index, int off) return index * PCPU_BITMAP_BLOCK_BITS + off; } +/* + * pcpu_next_hint - determine which hint to use + * @block: block of interest + * @alloc_bits: size of allocation + * + * This determines if we should scan based on the scan_hint or first_free. + * In general, we want to scan from first_free to fulfill allocations by + * first fit. However, if we know a scan_hint at position scan_hint_start + * cannot fulfill an allocation, we can begin scanning from there knowing + * the contig_hint will be our fallback. + */ +static int pcpu_next_hint(struct pcpu_block_md *block, int alloc_bits) +{ + /* + * The three conditions below determine if we can skip past the + * scan_hint. First, does the scan hint exist. Second, is the + * contig_hint after the scan_hint (possibly not true iff + * contig_hint == scan_hint). Third, is the allocation request + * larger than the scan_hint. + */ + if (block->scan_hint && + block->contig_hint_start > block->scan_hint_start && + alloc_bits > block->scan_hint) + return block->scan_hint_start + block->scan_hint; + + return block->first_free; +} + /** * pcpu_next_md_free_region - finds the next hint free area * @chunk: chunk of interest @@ -415,9 +443,11 @@ static void pcpu_next_fit_region(struct pcpu_chunk *chunk, int alloc_bits, if (block->contig_hint && block->contig_hint_start >= block_off && block->contig_hint >= *bits + alloc_bits) { + int start = pcpu_next_hint(block, alloc_bits); + *bits += alloc_bits + block->contig_hint_start - - block->first_free; - *bit_off = pcpu_block_off_to_off(i, block->first_free); + start; + *bit_off = pcpu_block_off_to_off(i, start); return; } /* reset to satisfy the second predicate above */ @@ -632,12 +662,57 @@ static void pcpu_block_update(struct pcpu_block_md *block, int start, int end) block->right_free = contig; if (contig > block->contig_hint) { + /* promote the old contig_hint to be the new scan_hint */ + if (start > block->contig_hint_start) { + if (block->contig_hint > block->scan_hint) { + block->scan_hint_start = + block->contig_hint_start; + block->scan_hint = block->contig_hint; + } else if (start < block->scan_hint_start) { + /* + * The old contig_hint == scan_hint. But, the + * new contig is larger so hold the invariant + * scan_hint_start < contig_hint_start. + */ + block->scan_hint = 0; + } + } else { + block->scan_hint = 0; + } block->contig_hint_start = start; block->contig_hint = contig; - } else if (block->contig_hint_start && contig == block->contig_hint && - (!start || __ffs(start) > __ffs(block->contig_hint_start))) { - /* use the start with the best alignment */ - block->contig_hint_start = start; + } else if (contig == block->contig_hint) { + if (block->contig_hint_start && + (!start || + __ffs(start) > __ffs(block->contig_hint_start))) { + /* start has a better alignment so use it */ + block->contig_hint_start = start; + if (start < block->scan_hint_start && + block->contig_hint > block->scan_hint) + block->scan_hint = 0; + } else if (start > block->scan_hint_start || + block->contig_hint > block->scan_hint) { + /* + * Knowing contig == contig_hint, update the scan_hint + * if it is farther than or larger than the current + * scan_hint. + */ + block->scan_hint_start = start; + block->scan_hint = contig; + } + } else { + /* + * The region is smaller than the contig_hint. So only update + * the scan_hint if it is larger than or equal and farther than + * the current scan_hint. + */ + if ((start < block->contig_hint_start && + (contig > block->scan_hint || + (contig == block->scan_hint && + start > block->scan_hint_start)))) { + block->scan_hint_start = start; + block->scan_hint = contig; + } } } @@ -656,7 +731,7 @@ static void pcpu_block_refresh_hint(struct pcpu_chunk *chunk, int index) int rs, re; /* region start, region end */ /* clear hints */ - block->contig_hint = 0; + block->contig_hint = block->scan_hint = 0; block->left_free = block->right_free = 0; /* iterate over free areas and update the contig hints */ @@ -713,6 +788,12 @@ static void pcpu_block_update_hint_alloc(struct pcpu_chunk *chunk, int bit_off, PCPU_BITMAP_BLOCK_BITS, s_off + bits); + if (pcpu_region_overlap(s_block->scan_hint_start, + s_block->scan_hint_start + s_block->scan_hint, + s_off, + s_off + bits)) + s_block->scan_hint = 0; + if (pcpu_region_overlap(s_block->contig_hint_start, s_block->contig_hint_start + s_block->contig_hint, @@ -749,6 +830,9 @@ static void pcpu_block_update_hint_alloc(struct pcpu_chunk *chunk, int bit_off, /* reset the block */ e_block++; } else { + if (e_off > e_block->scan_hint_start) + e_block->scan_hint = 0; + if (e_off > e_block->contig_hint_start) { /* contig hint is broken - scan to fix it */ pcpu_block_refresh_hint(chunk, e_index); @@ -763,6 +847,7 @@ static void pcpu_block_update_hint_alloc(struct pcpu_chunk *chunk, int bit_off, /* update in-between md_blocks */ nr_empty_pages += (e_index - s_index - 1); for (block = s_block + 1; block < e_block; block++) { + block->scan_hint = 0; block->contig_hint = 0; block->left_free = 0; block->right_free = 0; @@ -873,6 +958,7 @@ static void pcpu_block_update_hint_free(struct pcpu_chunk *chunk, int bit_off, nr_empty_pages += (e_index - s_index - 1); for (block = s_block + 1; block < e_block; block++) { block->first_free = 0; + block->scan_hint = 0; block->contig_hint_start = 0; block->contig_hint = PCPU_BITMAP_BLOCK_BITS; block->left_free = PCPU_BITMAP_BLOCK_BITS; @@ -1084,6 +1170,7 @@ static void pcpu_init_md_blocks(struct pcpu_chunk *chunk) for (md_block = chunk->md_blocks; md_block != chunk->md_blocks + pcpu_chunk_nr_blocks(chunk); md_block++) { + md_block->scan_hint = 0; md_block->contig_hint = PCPU_BITMAP_BLOCK_BITS; md_block->left_free = PCPU_BITMAP_BLOCK_BITS; md_block->right_free = PCPU_BITMAP_BLOCK_BITS;
Fragmentation can cause both blocks and chunks to have an early first_firee bit available, but only able to satisfy allocations much later on. This patch introduces a scan_hint to help mitigate some unnecessary scanning. The scan_hint remembers the largest area prior to the contig_hint. If the contig_hint == scan_hint, then scan_hint_start > contig_hint_start. This is necessary for scan_hint discovery when refreshing a block. Signed-off-by: Dennis Zhou <dennis@kernel.org> --- mm/percpu-internal.h | 9 ++++ mm/percpu.c | 101 ++++++++++++++++++++++++++++++++++++++++--- 2 files changed, 103 insertions(+), 7 deletions(-)