| Message ID | e3ae5bfc7cd4b640e83a25f001169d4ae50d797a.1687296675.git.osandov@osandov.com (mailing list archive) |
|---|---|
| State | Superseded, archived |
| Headers | show |
| Series | xfs: CPU usage optimizations for realtime allocator | expand |
On Tue, Jun 20, 2023 at 02:32:12PM -0700, Omar Sandoval wrote: > From: Omar Sandoval <osandov@fb.com> > > In commit 355e3532132b ("xfs: cache minimum realtime summary level"), I > added a cache of the minimum level of the realtime summary that has any > free extents. However, it turns out that the _maximum_ level is more > useful for upcoming optimizations, and basically equivalent for the > existing usage. So, let's change the meaning of the cache to be the > maximum level + 1, or 0 if there are no free extents. Hmm. If I'm reading xfs_rtmodify_summary_int right, m_rsum_cache[b] now tells us the maximum log2(length) of the free extents starting in rtbitmap block b? IOWs, let's say the cache contents are: {2, 3, 2, 15, 8} Someone asks for a 400rtx (realtime extent) allocation, so we want to find a free space of at least magnitude floor(log2(400)) == 8. The cache tells us that there aren't any free extents longer than 2^1 blocks in rtbitmap blocks 0 and 2; longer than 2^2 blocks in rtbmp block 1; longer than 2^7 blocks in rtbmp block 4; nor longer than 2^14 blocks in rtbmp block 3? From the cache contents, we should therefore examine rtbitmap block 3. If the cache contents were instead: {2, 3, 2, 8, 8} Then we instead might scan rtbitmap blocks 3 and 4 for the longest allocation that we can get? Looking back at the original commit, that seems to make more sense to me... > Signed-off-by: Omar Sandoval <osandov@fb.com> > --- > fs/xfs/libxfs/xfs_rtbitmap.c | 6 +++--- > fs/xfs/xfs_mount.h | 6 +++--- > fs/xfs/xfs_rtalloc.c | 31 +++++++++++++++++++------------ > 3 files changed, 25 insertions(+), 18 deletions(-) > > diff --git a/fs/xfs/libxfs/xfs_rtbitmap.c b/fs/xfs/libxfs/xfs_rtbitmap.c > index 1a832c9a412f..d9493f64adfc 100644 > --- a/fs/xfs/libxfs/xfs_rtbitmap.c > +++ b/fs/xfs/libxfs/xfs_rtbitmap.c > @@ -503,10 +503,10 @@ xfs_rtmodify_summary_int( > > *sp += delta; > if (mp->m_rsum_cache) { > - if (*sp == 0 && log == mp->m_rsum_cache[bbno]) > - mp->m_rsum_cache[bbno]++; > - if (*sp != 0 && log < mp->m_rsum_cache[bbno]) > + if (*sp == 0 && log + 1 == mp->m_rsum_cache[bbno]) > mp->m_rsum_cache[bbno] = log; > + if (*sp != 0 && log >= mp->m_rsum_cache[bbno]) > + mp->m_rsum_cache[bbno] = log + 1; > } > xfs_trans_log_buf(tp, bp, first, first + sizeof(*sp) - 1); > } > diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h > index 6c09f89534d3..964541c36730 100644 > --- a/fs/xfs/xfs_mount.h > +++ b/fs/xfs/xfs_mount.h > @@ -103,9 +103,9 @@ typedef struct xfs_mount { > > /* > * Optional cache of rt summary level per bitmap block with the > - * invariant that m_rsum_cache[bbno] <= the minimum i for which > - * rsum[i][bbno] != 0. Reads and writes are serialized by the rsumip > - * inode lock. > + * invariant that m_rsum_cache[bbno] > the maximum i for which > + * rsum[i][bbno] != 0, or 0 if rsum[i][bbno] == 0 for all i. > + * Reads and writes are serialized by the rsumip inode lock. > */ > uint8_t *m_rsum_cache; > struct xfs_mru_cache *m_filestream; /* per-mount filestream data */ > diff --git a/fs/xfs/xfs_rtalloc.c b/fs/xfs/xfs_rtalloc.c > index 61ef13286654..d3c76532d20e 100644 > --- a/fs/xfs/xfs_rtalloc.c > +++ b/fs/xfs/xfs_rtalloc.c > @@ -56,14 +56,19 @@ xfs_rtany_summary( > int log; /* loop counter, log2 of ext. size */ > xfs_suminfo_t sum; /* summary data */ > > - /* There are no extents at levels < m_rsum_cache[bbno]. */ > - if (mp->m_rsum_cache && low < mp->m_rsum_cache[bbno]) > - low = mp->m_rsum_cache[bbno]; > + /* There are no extents at levels >= m_rsum_cache[bbno]. */ > + if (mp->m_rsum_cache) { > + high = min(high, mp->m_rsum_cache[bbno] - 1); > + if (low > high) { > + *stat = 0; > + return 0; > + } > + } > > /* > * Loop over logs of extent sizes. > */ > - for (log = low; log <= high; log++) { > + for (log = high; log >= low; log--) { > /* > * Get one summary datum. > */ > @@ -84,9 +89,9 @@ xfs_rtany_summary( > */ > *stat = 0; > out: > - /* There were no extents at levels < log. */ > - if (mp->m_rsum_cache && log > mp->m_rsum_cache[bbno]) > - mp->m_rsum_cache[bbno] = log; > + /* There were no extents at levels > log. */ > + if (mp->m_rsum_cache && log + 1 < mp->m_rsum_cache[bbno]) > + mp->m_rsum_cache[bbno] = log + 1; > return 0; > } > > @@ -878,12 +883,14 @@ xfs_alloc_rsum_cache( > xfs_extlen_t rbmblocks) /* number of rt bitmap blocks */ > { > /* > - * The rsum cache is initialized to all zeroes, which is trivially a > - * lower bound on the minimum level with any free extents. We can > - * continue without the cache if it couldn't be allocated. > + * The rsum cache is initialized to the maximum value, which is > + * trivially an upper bound on the maximum level with any free extents. > + * We can continue without the cache if it couldn't be allocated. > */ > - mp->m_rsum_cache = kvzalloc(rbmblocks, GFP_KERNEL); > - if (!mp->m_rsum_cache) > + mp->m_rsum_cache = kvmalloc(rbmblocks, GFP_KERNEL); > + if (mp->m_rsum_cache) > + memset(mp->m_rsum_cache, -1, rbmblocks); > + else > xfs_warn(mp, "could not allocate realtime summary cache"); > } > > -- > 2.41.0 >
On Wed, Jul 12, 2023 at 03:40:01PM -0700, Darrick J. Wong wrote: > On Tue, Jun 20, 2023 at 02:32:12PM -0700, Omar Sandoval wrote: > > From: Omar Sandoval <osandov@fb.com> > > > > In commit 355e3532132b ("xfs: cache minimum realtime summary level"), I > > added a cache of the minimum level of the realtime summary that has any > > free extents. However, it turns out that the _maximum_ level is more > > useful for upcoming optimizations, and basically equivalent for the > > existing usage. So, let's change the meaning of the cache to be the > > maximum level + 1, or 0 if there are no free extents. > > Hmm. If I'm reading xfs_rtmodify_summary_int right, m_rsum_cache[b] now > tells us the maximum log2(length) of the free extents starting in > rtbitmap block b? > > IOWs, let's say the cache contents are: > > {2, 3, 2, 15, 8} > > Someone asks for a 400rtx (realtime extent) allocation, so we want to > find a free space of at least magnitude floor(log2(400)) == 8. > > The cache tells us that there aren't any free extents longer than 2^1 > blocks in rtbitmap blocks 0 and 2; longer than 2^2 blocks in rtbmp block > 1; longer than 2^7 blocks in rtbmp block 4; nor longer than 2^14 blocks > in rtbmp block 3? There's a potential for an off-by-one bug here, so just to make sure we're saying the same thing: the realtime summary for level n contains the number of free extents starting in a bitmap block such that floor(log2(size_in_realtime_extents)) == n. The maximum size of a free extent in level n is therefore 2^(n + 1) - 1 realtime extents. So in your example, the cache is telling us that realtime bitmap blocks 0 and 2 don't have anything free in levels 2 or above, and therefore don't have any free extents longer than _or equal to_ 2^2. I'll try to reword the commit message and comments to make this unambiguous.
On Mon, Jul 17, 2023 at 12:54:24PM -0700, Omar Sandoval wrote: > On Wed, Jul 12, 2023 at 03:40:01PM -0700, Darrick J. Wong wrote: > > On Tue, Jun 20, 2023 at 02:32:12PM -0700, Omar Sandoval wrote: > > > From: Omar Sandoval <osandov@fb.com> > > > > > > In commit 355e3532132b ("xfs: cache minimum realtime summary level"), I > > > added a cache of the minimum level of the realtime summary that has any > > > free extents. However, it turns out that the _maximum_ level is more > > > useful for upcoming optimizations, and basically equivalent for the > > > existing usage. So, let's change the meaning of the cache to be the > > > maximum level + 1, or 0 if there are no free extents. > > > > Hmm. If I'm reading xfs_rtmodify_summary_int right, m_rsum_cache[b] now > > tells us the maximum log2(length) of the free extents starting in > > rtbitmap block b? > > > > IOWs, let's say the cache contents are: > > > > {2, 3, 2, 15, 8} > > > > Someone asks for a 400rtx (realtime extent) allocation, so we want to > > find a free space of at least magnitude floor(log2(400)) == 8. > > > > The cache tells us that there aren't any free extents longer than 2^1 > > blocks in rtbitmap blocks 0 and 2; longer than 2^2 blocks in rtbmp block > > 1; longer than 2^7 blocks in rtbmp block 4; nor longer than 2^14 blocks > > in rtbmp block 3? > > There's a potential for an off-by-one bug here, so just to make sure > we're saying the same thing: the realtime summary for level n contains > the number of free extents starting in a bitmap block such that > floor(log2(size_in_realtime_extents)) == n. The maximum size of a free > extent in level n is therefore 2^(n + 1) - 1 realtime extents. > > So in your example, the cache is telling us that realtime bitmap blocks > 0 and 2 don't have anything free in levels 2 or above, and therefore > don't have any free extents longer than _or equal to_ 2^2. D'oh. I forgot that subtlety that the maximum size of a free extent in level n is therefore 2^(n + 1) - 1 realtime extents. > I'll try to reword the commit message and comments to make this > unambiguous. Ok, thanks. A couple of quick examples (feel free to use mine) would be helpful for descrambling my brain. :) --D
diff --git a/fs/xfs/libxfs/xfs_rtbitmap.c b/fs/xfs/libxfs/xfs_rtbitmap.c index 1a832c9a412f..d9493f64adfc 100644 --- a/fs/xfs/libxfs/xfs_rtbitmap.c +++ b/fs/xfs/libxfs/xfs_rtbitmap.c @@ -503,10 +503,10 @@ xfs_rtmodify_summary_int( *sp += delta; if (mp->m_rsum_cache) { - if (*sp == 0 && log == mp->m_rsum_cache[bbno]) - mp->m_rsum_cache[bbno]++; - if (*sp != 0 && log < mp->m_rsum_cache[bbno]) + if (*sp == 0 && log + 1 == mp->m_rsum_cache[bbno]) mp->m_rsum_cache[bbno] = log; + if (*sp != 0 && log >= mp->m_rsum_cache[bbno]) + mp->m_rsum_cache[bbno] = log + 1; } xfs_trans_log_buf(tp, bp, first, first + sizeof(*sp) - 1); } diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h index 6c09f89534d3..964541c36730 100644 --- a/fs/xfs/xfs_mount.h +++ b/fs/xfs/xfs_mount.h @@ -103,9 +103,9 @@ typedef struct xfs_mount { /* * Optional cache of rt summary level per bitmap block with the - * invariant that m_rsum_cache[bbno] <= the minimum i for which - * rsum[i][bbno] != 0. Reads and writes are serialized by the rsumip - * inode lock. + * invariant that m_rsum_cache[bbno] > the maximum i for which + * rsum[i][bbno] != 0, or 0 if rsum[i][bbno] == 0 for all i. + * Reads and writes are serialized by the rsumip inode lock. */ uint8_t *m_rsum_cache; struct xfs_mru_cache *m_filestream; /* per-mount filestream data */ diff --git a/fs/xfs/xfs_rtalloc.c b/fs/xfs/xfs_rtalloc.c index 61ef13286654..d3c76532d20e 100644 --- a/fs/xfs/xfs_rtalloc.c +++ b/fs/xfs/xfs_rtalloc.c @@ -56,14 +56,19 @@ xfs_rtany_summary( int log; /* loop counter, log2 of ext. size */ xfs_suminfo_t sum; /* summary data */ - /* There are no extents at levels < m_rsum_cache[bbno]. */ - if (mp->m_rsum_cache && low < mp->m_rsum_cache[bbno]) - low = mp->m_rsum_cache[bbno]; + /* There are no extents at levels >= m_rsum_cache[bbno]. */ + if (mp->m_rsum_cache) { + high = min(high, mp->m_rsum_cache[bbno] - 1); + if (low > high) { + *stat = 0; + return 0; + } + } /* * Loop over logs of extent sizes. */ - for (log = low; log <= high; log++) { + for (log = high; log >= low; log--) { /* * Get one summary datum. */ @@ -84,9 +89,9 @@ xfs_rtany_summary( */ *stat = 0; out: - /* There were no extents at levels < log. */ - if (mp->m_rsum_cache && log > mp->m_rsum_cache[bbno]) - mp->m_rsum_cache[bbno] = log; + /* There were no extents at levels > log. */ + if (mp->m_rsum_cache && log + 1 < mp->m_rsum_cache[bbno]) + mp->m_rsum_cache[bbno] = log + 1; return 0; } @@ -878,12 +883,14 @@ xfs_alloc_rsum_cache( xfs_extlen_t rbmblocks) /* number of rt bitmap blocks */ { /* - * The rsum cache is initialized to all zeroes, which is trivially a - * lower bound on the minimum level with any free extents. We can - * continue without the cache if it couldn't be allocated. + * The rsum cache is initialized to the maximum value, which is + * trivially an upper bound on the maximum level with any free extents. + * We can continue without the cache if it couldn't be allocated. */ - mp->m_rsum_cache = kvzalloc(rbmblocks, GFP_KERNEL); - if (!mp->m_rsum_cache) + mp->m_rsum_cache = kvmalloc(rbmblocks, GFP_KERNEL); + if (mp->m_rsum_cache) + memset(mp->m_rsum_cache, -1, rbmblocks); + else xfs_warn(mp, "could not allocate realtime summary cache"); }