mirror of
git://git.code.sf.net/p/sbcl/sbcl
synced 2026-09-10 07:26:40 -04:00
Always define page_words_t as 'unsigned short'
And rob 1 bit of that, so it's effectively 15 bits, not 16.
Then free up 2 more bits of 'type' for other use as I tried to do
in rev 938320b209 which was reverted. Taking a different bit in the
PTE should be fine, and the resulting code looks better for it.
This commit is contained in:
Douglas Katzman
parent
1a0a291c06
commit
3bfea7ffd3
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@ -829,9 +829,7 @@ Experimental: interface subject to change."
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(let* ((wp (page-protected-p object))
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(index (sb-vm:find-page-index
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(get-lisp-obj-address object)))
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(flags (sb-alien:slot page 'sb-vm::flags))
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(type #+little-endian (ldb (byte 6 0) flags)
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#+big-endian (ldb (byte 6 2) flags)))
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(type (sb-alien:slot page 'sb-vm::flags)))
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(list :space space
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:generation (sb-alien:slot page 'sb-vm::gen)
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:write-protected wp
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@ -483,14 +483,9 @@ statistics are appended to it."
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;; but if 64-bit then we have to scale the value. Additionally
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;; there is a fallback for when even the scaled value is too big.
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(sb-vm::start #+64-bit (unsigned 32) #-64-bit signed)
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;; On platforms with small enough GC pages, this field
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;; will be a short. On platforms with larger ones, it'll
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;; be an int. It should probably never be an int.
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(sb-vm::words-used (unsigned
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#.(if (typep sb-vm::gencgc-page-words '(unsigned-byte 16))
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16
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32)))
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(sb-vm::flags (unsigned 8)) ; in C this is {type, need_zerofill, pinned}
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;; Caution: The low bit of WORDS-USED* is a flag bit
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(sb-vm::words-used* (unsigned 16)) ; (* in the name is a memory aid)
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(sb-vm::flags (unsigned 8)) ; this named 'type' in C
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(sb-vm::gen (signed 8))))
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(define-alien-variable ("page_table" sb-vm:page-table) (* (struct sb-vm::page)))
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(declaim (inline sb-vm:find-page-index))
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@ -386,7 +386,8 @@ We could try a few things to mitigate this:
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start-page end-page))
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(setq end-page start-page)
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(loop (setq end-page-bytes-used
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(ash (slot (deref page-table end-page) 'words-used) word-shift))
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(ash (ash (slot (deref page-table end-page) 'words-used*) -1)
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word-shift))
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;; See 'page_ends_contiguous_block_p' in gencgc.c
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(when (or (< end-page-bytes-used gencgc-page-bytes)
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(= (slot (deref page-table (1+ end-page)) 'start) 0))
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@ -400,10 +401,7 @@ We could try a few things to mitigate this:
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end-page-bytes-used)
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most-positive-word)))))
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(when (sap> end start)
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;; The bits in the 6-bit 'type' field have fixed positions,
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;; but the position of the field itself depends on endianness.
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(let ((flags (ldb (byte 6 (+ #+big-endian 2))
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(slot (deref page-table start-page) 'flags))))
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(let ((flags (slot (deref page-table start-page) 'flags)))
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;; The GEN slot is declared as (SIGNED 8) which does not satisfy the
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;; type restriction on the first argument to LOGBITP.
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;; Masking it to 3 bits fixes that, and allows using the other 5 bits
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@ -1157,8 +1155,8 @@ We could try a few things to mitigate this:
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(setq page-num next-page seen-filler nil))))))))
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(let ((i 0))
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(loop while (< i total-pages)
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do (let ((type (ldb (byte 2 0) (slot (deref page-table i) 'flags))))
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(if (= type 3)
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do (let ((type (slot (deref page-table i) 'flags)))
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(if (= (logand type 7) 7)
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(setq i (dump-page i))
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(incf i)))))
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(let* ((n-pages (count 1 pages))
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@ -1227,8 +1225,7 @@ We could try a few things to mitigate this:
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;; gen0 conses on MIXED pages, but even that is not enough- pinned conses
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;; will promote but keep their MIXED page type. So don't bother with this.
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#+use-cons-region
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(let* ((flags (slot (deref page-table (find-page-index obj-addr)) 'flags))
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(type (ldb (byte 6 (+ #+big-endian 2)) flags))
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(let* ((type (slot (deref page-table (find-page-index obj-addr)) 'flags))
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(ok (if (consp obj)
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(or (= type #b101) ; PAGE_TYPE_CONS
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(and (eq (car obj) 0) (eq (cdr obj) 0)))
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@ -48,15 +48,16 @@ int gencgc_handle_wp_violation(void*, void*);
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# define CONDENSED_PAGE_TABLE 0
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#endif
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#if GENCGC_PAGE_WORDS > USHRT_MAX
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# if GENCGC_PAGE_WORDS > UINT_MAX
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/* One bit of page_words_t is the need_zerofill flag.
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* That leaves 15 bits to store page_words_used. This can represent
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* a page size of up to 64KiB on 32-bit and 128KiB on 64-bit.
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* Note that since the allocation quantum is actually 2 words
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* the words_used is always an even number, and so technically
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* we could store as "dualwords used" to achieve double the range */
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#if GENCGC_PAGE_WORDS > 32767
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# error "GENCGC_PAGE_WORDS unexpectedly large."
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# else
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typedef unsigned int page_words_t;
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# endif
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#else
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typedef unsigned short page_words_t;
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#endif
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typedef unsigned short page_words_t;
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/* New objects are allocated to PAGE_TYPE_MIXED or PAGE_TYPE_CONS */
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/* If you change these constants, then possibly also change the following
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@ -114,14 +115,22 @@ struct page {
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/* the number of lispwords of this page that are used. This may be less
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* than the usage at an instant in time for pages within the current
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* allocation regions. MUST be 0 for unallocated pages.
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*/
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page_words_t words_used_;
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* allocation regions. The 0th bit of the physical uint16 indicates
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* that the page needs to be zero-filled for the next use.
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* Let the C compiler figure it out, so we can't get it wrong in C.
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* But we need to reverse the order of the packed fields depending on
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* endianness so that the Lisp side is easier to understand */
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#ifdef LISP_FEATURE_BIG_ENDIAN
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page_words_t words_used_ : 15;
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page_words_t need_zerofill : 1;
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#else
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page_words_t need_zerofill : 1;
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page_words_t words_used_ : 15;
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#endif
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// !!! If bit positions are changed, be sure to reflect the changes into
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// page_extensible_p() as well as ALLOCATION-INFORMATION in sb-introspect
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// and WALK-DYNAMIC-SPACE.
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unsigned char
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/*
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* The 4 low bits of 'type' are defined by PAGE_TYPE_x constants.
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* 0000 free
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@ -129,12 +138,12 @@ struct page {
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* ?010 strictly unboxed data
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* ?011 mixed boxed/unboxed non-code objects
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* ?111 code
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* The next two bits are SINGLE_OBJECT and OPEN_REGION */
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type :6,
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/* Whether the page was used at all. This is the only bit that can
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* be 1 on a free page */
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need_zerofill :1,
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dontuse :1;
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* The next two bits are SINGLE_OBJECT and OPEN_REGION.
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* The top two can be used for segregating objects by widetag
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* which will important once we have "destructors" to run for a
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* for a category of object, such as SYMBOL, hypothetically for
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* recycling TLS indices or something like that. */
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unsigned char type;
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/* the generation that this page belongs to. This should be valid
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* for all pages that may have objects allocated, even current
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@ -220,7 +220,6 @@ static inline void reset_page_flags(page_index_t page) {
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if (page_table[page].type == PAGE_TYPE_CODE) set_page_need_to_zero(page, 1);
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#endif
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page_table[page].type = 0;
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page_table[page].dontuse = 0;
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gc_page_pins[page] = 0;
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// Why can't the 'gen' get cleared? It caused failures. THIS MAKES NO SENSE!!!
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// page_table[page].gen = 0;
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@ -955,18 +954,8 @@ page_extensible_p(page_index_t index, generation_index_t gen, int type) {
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&& page_table[index].gen == gen
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&& !gc_page_pins[index];
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#else
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/* Test the three conditions above as a single comparison.
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*
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* pin -\
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* v vvvvvv -- type
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* #b11111111_10111111
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* ^
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* need_zerofill (ignored)
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*
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* The flags reside at 1 byte prior to 'gen' in the page structure.
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*/
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int attributes_match =
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(*(int16_t*)(&page_table[index].gen-1) & 0xFFBF) == ((gen<<8)|type);
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*(int16_t*)&page_table[index].type == ((gen<<8)|type);
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#endif
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#ifdef LISP_FEATURE_SOFT_CARD_MARKS
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return attributes_match && page_cards_all_marked_nonsticky(index);
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@ -41,9 +41,8 @@
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(declare (ignore widetag))
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(let* ((index
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(sb-vm::find-page-index (sb-kernel:get-lisp-obj-address obj)))
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(type (ldb (byte 6 (+ #+big-endian 2))
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(sb-alien:slot (sb-alien:deref sb-vm::page-table index)
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'sb-vm::flags))))
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(type (sb-alien:slot (sb-alien:deref sb-vm::page-table index)
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'sb-vm::flags)))
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;; mask off the SINGLE_OBJECT and OPEN_REGION bits
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(when (and (eq (logand type 7) 2) ; PAGE_TYPE_BOXED
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;; Cons cells on boxed pags are page filler
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@ -33,9 +33,10 @@
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#+gencgc
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(progn
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(defun page-words-used (index)
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(ash (slot (deref sb-vm::page-table index) 'sb-vm::words-used*) -1))
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(defun page-need-to-zero (index)
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(logbitp #+little-endian 6 #+big-endian 1
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(slot (deref sb-vm::page-table index) 'sb-vm::flags)))
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(oddp (slot (deref sb-vm::page-table index) 'sb-vm::words-used*)))
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(defun test-private-consing ()
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(let ((conses-per-page ; subtract one for the page header cons
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(1- (/ sb-vm:gencgc-page-bytes (* 2 sb-vm:n-word-bytes))))
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@ -51,7 +52,7 @@
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(push index pages)
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(assert (= cons (+ base-address (* 2 sb-vm:n-word-bytes))))
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;; words-used should be 4, for 2 conses,
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(assert (= (slot (deref sb-vm::page-table index) 'sb-vm::words-used) 4))
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(assert (= (page-words-used index) 4))
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(dotimes (i (1- conses-per-page))
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(setq final (private-list (incf counter))))
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(assert (= final (+ base-address sb-vm:gencgc-page-bytes
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@ -70,7 +71,7 @@
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;; Each of the pages should have zero words used and need-to-zero = 1
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(dolist (index pages)
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(assert (page-need-to-zero index))
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(assert (= (slot (deref sb-vm::page-table index) 'sb-vm::words-used) 0))))))
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(assert (= (page-words-used index) 0))))))
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#-gencgc
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(defun test-private-consing ()
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