| Message ID | 20230515113344.6869-5-mgorman@techsingularity.net (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Follow-up "Fix excessive CPU usage during compaction" | expand |
On 5/15/23 13:33, Mel Gorman wrote: > This reverts commit 95e7a450b819 ("Revert "mm/compaction: fix set skip > in fast_find_migrateblock""). > > Commit 7efc3b726103 ("mm/compaction: fix set skip in fast_find_migrateblock") > was reverted due to bug reports about khugepaged consuming large amounts > of CPU without making progress. The underlying bug was partially fixed > by commit cfccd2e63e7e ("mm, compaction: finish pageblocks on complete > migration failure") but it only mitigated the problem and Vlastimil Babka > pointing out the same issue could theoretically happen to kcompactd. > > As pageblocks containing pages that fail to migrate should now be > forcibly rescanned to set the skip hint if skip hints are used, > fast_find_migrateblock() should no longer loop on a small subset > of pageblocks for prolonged periods of time. Revert the revert so > fast_find_migrateblock() is effective again. > > Using the mmtests config workload-usemem-stress-numa-compact, the number > of unique ranges scanned was analysed for both kcompactd and !kcompactd > activity. > > 6.4.0-rc1-vanilla > kcompactd > 7 range=(0x10d600~0x10d800) > 7 range=(0x110c00~0x110e00) > 7 range=(0x110e00~0x111000) > 7 range=(0x111800~0x111a00) > 7 range=(0x111a00~0x111c00) > !kcompactd > 1 range=(0x113e00~0x114000) > 1 range=(0x114000~0x114020) > 1 range=(0x114400~0x114489) > 1 range=(0x114489~0x1144aa) > 1 range=(0x1144aa~0x114600) > > 6.4.0-rc1-mm-revertfastmigrate > kcompactd > 17 range=(0x104200~0x104400) > 17 range=(0x104400~0x104600) > 17 range=(0x104600~0x104800) > 17 range=(0x104800~0x104a00) > 17 range=(0x104a00~0x104c00) > !kcompactd > 1793 range=(0x15c200~0x15c400) > 5436 range=(0x105800~0x105a00) > 19826 range=(0x150a00~0x150c00) > 19833 range=(0x150800~0x150a00) > 19834 range=(0x11ce00~0x11d000) > > 6.4.0-rc1-mm-follupfastfind > kcompactd > 22 range=(0x107200~0x107400) > 23 range=(0x107400~0x107600) > 23 range=(0x107600~0x107800) > 23 range=(0x107c00~0x107e00) > 23 range=(0x107e00~0x108000) > !kcompactd > 3 range=(0x890240~0x890400) > 5 range=(0x886e00~0x887000) > 5 range=(0x88a400~0x88a600) > 6 range=(0x88f800~0x88fa00) > 9 range=(0x88a400~0x88a420) > > Note that the vanilla kernel and the full series had some duplication of > ranges scanned but it was not severe and would be in line with compaction > resets when the skip hints are cleared. Just a revert of commit 7efc3b726103 > ("mm/compaction: fix set skip in fast_find_migrateblock") showed excessive > rescans of the same ranges so the series should not reintroduce bug 1206848. > > Link: https://bugzilla.suse.com/show_bug.cgi?id=1206848 > Signed-off-by: Mel Gorman <mgorman@techsingularity.net> My concerns about patch 3/4 don't affect this part so Acked-by: Vlastimil Babka <vbabka@suse.cz> > --- > mm/compaction.c | 1 - > 1 file changed, 1 deletion(-) > > diff --git a/mm/compaction.c b/mm/compaction.c > index d7be990b1d60..91af6a8b7a98 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -1859,7 +1859,6 @@ static unsigned long fast_find_migrateblock(struct compact_control *cc) > pfn = cc->zone->zone_start_pfn; > cc->fast_search_fail = 0; > found_block = true; > - set_pageblock_skip(freepage); > break; > } > }
diff --git a/mm/compaction.c b/mm/compaction.c index d7be990b1d60..91af6a8b7a98 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -1859,7 +1859,6 @@ static unsigned long fast_find_migrateblock(struct compact_control *cc) pfn = cc->zone->zone_start_pfn; cc->fast_search_fail = 0; found_block = true; - set_pageblock_skip(freepage); break; } }
This reverts commit 95e7a450b819 ("Revert "mm/compaction: fix set skip in fast_find_migrateblock""). Commit 7efc3b726103 ("mm/compaction: fix set skip in fast_find_migrateblock") was reverted due to bug reports about khugepaged consuming large amounts of CPU without making progress. The underlying bug was partially fixed by commit cfccd2e63e7e ("mm, compaction: finish pageblocks on complete migration failure") but it only mitigated the problem and Vlastimil Babka pointing out the same issue could theoretically happen to kcompactd. As pageblocks containing pages that fail to migrate should now be forcibly rescanned to set the skip hint if skip hints are used, fast_find_migrateblock() should no longer loop on a small subset of pageblocks for prolonged periods of time. Revert the revert so fast_find_migrateblock() is effective again. Using the mmtests config workload-usemem-stress-numa-compact, the number of unique ranges scanned was analysed for both kcompactd and !kcompactd activity. 6.4.0-rc1-vanilla kcompactd 7 range=(0x10d600~0x10d800) 7 range=(0x110c00~0x110e00) 7 range=(0x110e00~0x111000) 7 range=(0x111800~0x111a00) 7 range=(0x111a00~0x111c00) !kcompactd 1 range=(0x113e00~0x114000) 1 range=(0x114000~0x114020) 1 range=(0x114400~0x114489) 1 range=(0x114489~0x1144aa) 1 range=(0x1144aa~0x114600) 6.4.0-rc1-mm-revertfastmigrate kcompactd 17 range=(0x104200~0x104400) 17 range=(0x104400~0x104600) 17 range=(0x104600~0x104800) 17 range=(0x104800~0x104a00) 17 range=(0x104a00~0x104c00) !kcompactd 1793 range=(0x15c200~0x15c400) 5436 range=(0x105800~0x105a00) 19826 range=(0x150a00~0x150c00) 19833 range=(0x150800~0x150a00) 19834 range=(0x11ce00~0x11d000) 6.4.0-rc1-mm-follupfastfind kcompactd 22 range=(0x107200~0x107400) 23 range=(0x107400~0x107600) 23 range=(0x107600~0x107800) 23 range=(0x107c00~0x107e00) 23 range=(0x107e00~0x108000) !kcompactd 3 range=(0x890240~0x890400) 5 range=(0x886e00~0x887000) 5 range=(0x88a400~0x88a600) 6 range=(0x88f800~0x88fa00) 9 range=(0x88a400~0x88a420) Note that the vanilla kernel and the full series had some duplication of ranges scanned but it was not severe and would be in line with compaction resets when the skip hints are cleared. Just a revert of commit 7efc3b726103 ("mm/compaction: fix set skip in fast_find_migrateblock") showed excessive rescans of the same ranges so the series should not reintroduce bug 1206848. Link: https://bugzilla.suse.com/show_bug.cgi?id=1206848 Signed-off-by: Mel Gorman <mgorman@techsingularity.net> --- mm/compaction.c | 1 - 1 file changed, 1 deletion(-)