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63 lines
2.6 KiB
63 lines
2.6 KiB
Description: Make trimming logic consistent. |
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Author: Carlos O'Donell |
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Origin: git://sourceware.org/git/glibc.git |
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Bug-RHEL: N/A |
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Bug-Fedora: N/A |
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Bug-Upstream: #17195 |
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Upstream status: committed |
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commit e4bc326dbbf7328775fe7dd39de1178821363e0a |
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Author: Carlos O'Donell <carlos@systemhalted.org> |
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Date: Wed Oct 7 22:21:36 2015 -0400 |
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malloc: Consistently apply trim_threshold to all heaps (Bug 17195) |
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In the per-thread arenas we apply trim_threshold-based checks |
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to the extra space between the pad and the top_area. This isn't |
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quite accurate and instead we should be harmonizing with the way |
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in which trim_treshold is applied everywhere else like sysrtim |
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and _int_free. The trimming check should be based on the size of |
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the top chunk and only the size of the top chunk. The following |
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patch harmonizes the trimming and make it consistent for the main |
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arena and thread arenas. |
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In the old code a large padding request might have meant that |
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trimming was not triggered. Now trimming is considered first based |
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on the chunk, then the pad is subtracted, and the remainder trimmed. |
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This is how all the other trimmings operate. I didn't measure the |
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performance difference of this change because it corrects what I |
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consider to be a behavioural anomaly. We'll need some profile driven |
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optimization to make this code better, and even there Ondrej and |
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others have better ideas on how to speedup malloc. |
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Tested on x86_64 with no regressions. Already reviewed by Siddhesh |
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Poyarekar and Mel Gorman here and discussed here: |
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https://sourceware.org/ml/libc-alpha/2015-05/msg00002.html |
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Index: glibc-2.17-c758a686/malloc/arena.c |
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=================================================================== |
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--- glibc-2.17-c758a686.orig/malloc/arena.c |
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+++ glibc-2.17-c758a686/malloc/arena.c |
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@@ -697,14 +697,20 @@ heap_trim(heap_info *heap, size_t pad) |
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} |
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/* Uses similar logic for per-thread arenas as the main arena with systrim |
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- by preserving the top pad and at least a page. */ |
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+ and _int_free by preserving the top pad and rounding down to the nearest |
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+ page. */ |
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top_size = chunksize(top_chunk); |
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+ if ((unsigned long)(top_size) < |
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+ (unsigned long)(mp_.trim_threshold)) |
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+ return 0; |
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+ |
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top_area = top_size - MINSIZE - 1; |
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if (top_area <= pad) |
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return 0; |
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+ /* Release in pagesize units and round down to the nearest page. */ |
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extra = ALIGN_DOWN(top_area - pad, pagesz); |
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- if ((unsigned long) extra < mp_.trim_threshold) |
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+ if (extra == 0) |
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return 0; |
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/* Try to shrink. */ |
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if(shrink_heap(heap, extra) != 0)
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