cregit-Linux how code gets into the kernel

Release 4.11 fs/exofs/ore_raid.c

Directory: fs/exofs
/*
 * Copyright (C) 2011
 * Boaz Harrosh <ooo@electrozaur.com>
 *
 * This file is part of the objects raid engine (ore).
 *
 * It is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as published
 * by the Free Software Foundation.
 *
 * You should have received a copy of the GNU General Public License
 * along with "ore". If not, write to the Free Software Foundation, Inc:
 *      "Free Software Foundation <info@fsf.org>"
 */

#include <linux/gfp.h>
#include <linux/async_tx.h>

#include "ore_raid.h"


#undef ORE_DBGMSG2

#define ORE_DBGMSG2 ORE_DBGMSG


static struct page *_raid_page_alloc(void) { return alloc_page(GFP_KERNEL); }

Contributors

PersonTokensPropCommitsCommitProp
Boaz Harrosh1593.75%150.00%
Rashika Kheria16.25%150.00%
Total16100.00%2100.00%


static void _raid_page_free(struct page *p) { __free_page(p); }

Contributors

PersonTokensPropCommitsCommitProp
Boaz Harrosh1593.75%150.00%
Rashika Kheria16.25%150.00%
Total16100.00%2100.00%

/* This struct is forward declare in ore_io_state, but is private to here. * It is put on ios->sp2d for RAID5/6 writes only. See _gen_xor_unit. * * __stripe_pages_2d is a 2d array of pages, and it is also a corner turn. * Ascending page index access is sp2d(p-minor, c-major). But storage is * sp2d[p-minor][c-major], so it can be properlly presented to the async-xor * API. */ struct __stripe_pages_2d { /* Cache some hot path repeated calculations */ unsigned parity; unsigned data_devs; unsigned pages_in_unit; bool needed ; /* Array size is pages_in_unit (layout->stripe_unit / PAGE_SIZE) */ struct __1_page_stripe { bool alloc; unsigned write_count; struct async_submit_ctl submit; struct dma_async_tx_descriptor *tx; /* The size of this array is data_devs + parity */ struct page **pages; struct page **scribble; /* bool array, size of this array is data_devs */ char *page_is_read; } _1p_stripes[]; }; /* This can get bigger then a page. So support multiple page allocations * _sp2d_free should be called even if _sp2d_alloc fails (by returning * none-zero). */
static int _sp2d_alloc(unsigned pages_in_unit, unsigned group_width, unsigned parity, struct __stripe_pages_2d **psp2d) { struct __stripe_pages_2d *sp2d; unsigned data_devs = group_width - parity; struct _alloc_all_bytes { struct __alloc_stripe_pages_2d { struct __stripe_pages_2d sp2d; struct __1_page_stripe _1p_stripes[pages_in_unit]; } __asp2d; struct __alloc_1p_arrays { struct page *pages[group_width]; struct page *scribble[group_width]; char page_is_read[data_devs]; } __a1pa[pages_in_unit]; } *_aab; struct __alloc_1p_arrays *__a1pa; struct __alloc_1p_arrays *__a1pa_end; const unsigned sizeof__a1pa = sizeof(_aab->__a1pa[0]); unsigned num_a1pa, alloc_size, i; /* FIXME: check these numbers in ore_verify_layout */ BUG_ON(sizeof(_aab->__asp2d) > PAGE_SIZE); BUG_ON(sizeof__a1pa > PAGE_SIZE); if (sizeof(*_aab) > PAGE_SIZE) { num_a1pa = (PAGE_SIZE - sizeof(_aab->__asp2d)) / sizeof__a1pa; alloc_size = sizeof(_aab->__asp2d) + sizeof__a1pa * num_a1pa; } else { num_a1pa = pages_in_unit; alloc_size = sizeof(*_aab); } _aab = kzalloc(alloc_size, GFP_KERNEL); if (unlikely(!_aab)) { ORE_DBGMSG("!! Failed to alloc sp2d size=%d\n", alloc_size); return -ENOMEM; } sp2d = &_aab->__asp2d.sp2d; *psp2d = sp2d; /* From here Just call _sp2d_free */ __a1pa = _aab->__a1pa; __a1pa_end = __a1pa + num_a1pa; for (i = 0; i < pages_in_unit; ++i) { if (unlikely(__a1pa >= __a1pa_end)) { num_a1pa = min_t(unsigned, PAGE_SIZE / sizeof__a1pa, pages_in_unit - i); __a1pa = kcalloc(num_a1pa, sizeof__a1pa, GFP_KERNEL); if (unlikely(!__a1pa)) { ORE_DBGMSG("!! Failed to _alloc_1p_arrays=%d\n", num_a1pa); return -ENOMEM; } __a1pa_end = __a1pa + num_a1pa; /* First *pages is marked for kfree of the buffer */ sp2d->_1p_stripes[i].alloc = true; } sp2d->_1p_stripes[i].pages = __a1pa->pages; sp2d->_1p_stripes[i].scribble = __a1pa->scribble ; sp2d->_1p_stripes[i].page_is_read = __a1pa->page_is_read; ++__a1pa; } sp2d->parity = parity; sp2d->data_devs = data_devs; sp2d->pages_in_unit = pages_in_unit; return 0; }

Contributors

PersonTokensPropCommitsCommitProp
Boaz Harrosh40399.51%266.67%
Fabian Frederick20.49%133.33%
Total405100.00%3100.00%


static void _sp2d_reset(struct __stripe_pages_2d *sp2d, const struct _ore_r4w_op *r4w, void *priv) { unsigned data_devs = sp2d->data_devs; unsigned group_width = data_devs + sp2d->parity; int p, c; if (!sp2d->needed) return; for (c = data_devs - 1; c >= 0; --c) for (p = sp2d->pages_in_unit - 1; p >= 0; --p) { struct __1_page_stripe *_1ps = &sp2d->_1p_stripes[p]; if (_1ps->page_is_read[c]) { struct page *page = _1ps->pages[c]; r4w->put_page(priv, page); _1ps->page_is_read[c] = false; } } for (p = 0; p < sp2d->pages_in_unit; p++) { struct __1_page_stripe *_1ps = &sp2d->_1p_stripes[p]; memset(_1ps->pages, 0, group_width * sizeof(*_1ps->pages)); _1ps->write_count = 0; _1ps->tx = NULL; } sp2d->needed = false; }

Contributors

PersonTokensPropCommitsCommitProp
Boaz Harrosh205100.00%2100.00%
Total205100.00%2100.00%


static void _sp2d_free(struct __stripe_pages_2d *sp2d) { unsigned i; if (!sp2d) return; for (i = 0; i < sp2d->pages_in_unit; ++i) { if (sp2d->_1p_stripes[i].alloc) kfree(sp2d->_1p_stripes[i].pages); } kfree(sp2d); }

Contributors

PersonTokensPropCommitsCommitProp
Boaz Harrosh65100.00%1100.00%
Total65100.00%1100.00%


static unsigned _sp2d_min_pg(struct __stripe_pages_2d *sp2d) { unsigned p; for (p = 0; p < sp2d->pages_in_unit; p++) { struct __1_page_stripe *_1ps = &sp2d->_1p_stripes[p]; if (_1ps->write_count) return p; } return ~0; }

Contributors

PersonTokensPropCommitsCommitProp
Boaz Harrosh57100.00%1100.00%
Total57100.00%1100.00%


static unsigned _sp2d_max_pg(struct __stripe_pages_2d *sp2d) { int p; for (p = sp2d->pages_in_unit - 1; p >= 0; --p) { struct __1_page_stripe *_1ps = &sp2d->_1p_stripes[p]; if (_1ps->write_count) return p; } return ~0; }

Contributors

PersonTokensPropCommitsCommitProp
Boaz Harrosh5898.31%150.00%
Dan Carpenter11.69%150.00%
Total59100.00%2100.00%


static void _gen_xor_unit(struct __stripe_pages_2d *sp2d) { unsigned p; unsigned tx_flags = ASYNC_TX_ACK; if (sp2d->parity == 1) tx_flags |= ASYNC_TX_XOR_ZERO_DST; for (p = 0; p < sp2d->pages_in_unit; p++) { struct __1_page_stripe *_1ps = &sp2d->_1p_stripes[p]; if (!_1ps->write_count) continue; init_async_submit(&_1ps->submit, tx_flags, NULL, NULL, NULL, (addr_conv_t *)_1ps->scribble); if (sp2d->parity == 1) _1ps->tx = async_xor(_1ps->pages[sp2d->data_devs], _1ps->pages, 0, sp2d->data_devs, PAGE_SIZE, &_1ps->submit); else /* parity == 2 */ _1ps->tx = async_gen_syndrome(_1ps->pages, 0, sp2d->data_devs + sp2d->parity, PAGE_SIZE, &_1ps->submit); } for (p = 0; p < sp2d->pages_in_unit; p++) { struct __1_page_stripe *_1ps = &sp2d->_1p_stripes[p]; /* NOTE: We wait for HW synchronously (I don't have such HW * to test with.) Is parallelism needed with today's multi * cores? */ async_tx_issue_pending(_1ps->tx); } }

Contributors

PersonTokensPropCommitsCommitProp
Boaz Harrosh202100.00%2100.00%
Total202100.00%2100.00%


void _ore_add_stripe_page(struct __stripe_pages_2d *sp2d, struct ore_striping_info *si, struct page *page) { struct __1_page_stripe *_1ps; sp2d->needed = true; _1ps = &sp2d->_1p_stripes[si->cur_pg]; _1ps->pages[si->cur_comp] = page; ++_1ps->write_count; si->cur_pg = (si->cur_pg + 1) % sp2d->pages_in_unit; /* si->cur_comp is advanced outside at main loop */ }

Contributors

PersonTokensPropCommitsCommitProp
Boaz Harrosh76100.00%1100.00%
Total76100.00%1100.00%


void _ore_add_sg_seg(struct ore_per_dev_state *per_dev, unsigned cur_len, bool not_last) { struct osd_sg_entry *sge; ORE_DBGMSG("dev=%d cur_len=0x%x not_last=%d cur_sg=%d " "offset=0x%llx length=0x%x last_sgs_total=0x%x\n", per_dev->dev, cur_len, not_last, per_dev->cur_sg, _LLU(per_dev->offset), per_dev->length, per_dev->last_sgs_total); if (!per_dev->cur_sg) { sge = per_dev->sglist; /* First time we prepare two entries */ if (per_dev->length) { ++per_dev->cur_sg; sge->offset = per_dev->offset; sge->len = per_dev->length; } else { /* Here the parity is the first unit of this object. * This happens every time we reach a parity device on * the same stripe as the per_dev->offset. We need to * just skip this unit. */ per_dev->offset += cur_len; return; } } else { /* finalize the last one */ sge = &per_dev->sglist[per_dev->cur_sg - 1]; sge->len = per_dev->length - per_dev->last_sgs_total; } if (not_last) { /* Partly prepare the next one */ struct osd_sg_entry *next_sge = sge + 1; ++per_dev->cur_sg; next_sge->offset = sge->offset + sge->len + cur_len; /* Save cur len so we know how mutch was added next time */ per_dev->last_sgs_total = per_dev->length; next_sge->len = 0; } else if (!sge->len) { /* Optimize for when the last unit is a parity */ --per_dev->cur_sg; } }

Contributors

PersonTokensPropCommitsCommitProp
Boaz Harrosh206100.00%1100.00%
Total206100.00%1100.00%


static int _alloc_read_4_write(struct ore_io_state *ios) { struct ore_layout *layout = ios->layout; int ret; /* We want to only read those pages not in cache so worst case * is a stripe populated with every other page */ unsigned sgs_per_dev = ios->sp2d->pages_in_unit + 2; ret = _ore_get_io_state(layout, ios->oc, layout->group_width * layout->mirrors_p1, sgs_per_dev, 0, &ios->ios_read_4_write); return ret; }

Contributors

PersonTokensPropCommitsCommitProp
Boaz Harrosh66100.00%1100.00%
Total66100.00%1100.00%

/* @si contains info of the to-be-inserted page. Update of @si should be * maintained by caller. Specificaly si->dev, si->obj_offset, ... */
static int _add_to_r4w(struct ore_io_state *ios, struct ore_striping_info *si, struct page *page, unsigned pg_len) { struct request_queue *q; struct ore_per_dev_state *per_dev; struct ore_io_state *read_ios; unsigned first_dev = si->dev - (si->dev % (ios->layout->group_width * ios->layout->mirrors_p1)); unsigned comp = si->dev - first_dev; unsigned added_len; if (!ios->ios_read_4_write) { int ret = _alloc_read_4_write(ios); if (unlikely(ret)) return ret; } read_ios = ios->ios_read_4_write; read_ios->numdevs = ios->layout->group_width * ios->layout->mirrors_p1; per_dev = &read_ios->per_dev[comp]; if (!per_dev->length) { per_dev->bio = bio_kmalloc(GFP_KERNEL, ios->sp2d->pages_in_unit); if (unlikely(!per_dev->bio)) { ORE_DBGMSG("Failed to allocate BIO size=%u\n", ios->sp2d->pages_in_unit); return -ENOMEM; } per_dev->offset = si->obj_offset; per_dev->dev = si->dev; } else if (si->obj_offset != (per_dev->offset + per_dev->length)) { u64 gap = si->obj_offset - (per_dev->offset + per_dev->length); _ore_add_sg_seg(per_dev, gap, true); } q = osd_request_queue(ore_comp_dev(read_ios->oc, per_dev->dev)); added_len = bio_add_pc_page(q, per_dev->bio, page, pg_len, si->obj_offset % PAGE_SIZE); if (unlikely(added_len != pg_len)) { ORE_DBGMSG("Failed to bio_add_pc_page bi_vcnt=%d\n", per_dev->bio->bi_vcnt); return -ENOMEM; } per_dev->length += pg_len; return 0; }

Contributors

PersonTokensPropCommitsCommitProp
Boaz Harrosh321100.00%2100.00%
Total321100.00%2100.00%

/* read the beginning of an unaligned first page */
static int _add_to_r4w_first_page(struct ore_io_state *ios, struct page *page) { struct ore_striping_info si; unsigned pg_len; ore_calc_stripe_info(ios->layout, ios->offset, 0, &si); pg_len = si.obj_offset % PAGE_SIZE; si.obj_offset -= pg_len; ORE_DBGMSG("offset=0x%llx len=0x%x index=0x%lx dev=%x\n", _LLU(si.obj_offset), pg_len, page->index, si.dev); return _add_to_r4w(ios, &si, page, pg_len); }

Contributors

PersonTokensPropCommitsCommitProp
Boaz Harrosh88100.00%2100.00%
Total88100.00%2100.00%

/* read the end of an incomplete last page */
static int _add_to_r4w_last_page(struct ore_io_state *ios, u64 *offset) { struct ore_striping_info si; struct page *page; unsigned pg_len, p, c; ore_calc_stripe_info(ios->layout, *offset, 0, &si); p = si.cur_pg; c = si.cur_comp; page = ios->sp2d->_1p_stripes[p].pages[c]; pg_len = PAGE_SIZE - (si.unit_off % PAGE_SIZE); *offset += pg_len; ORE_DBGMSG("p=%d, c=%d next-offset=0x%llx len=0x%x dev=%x par_dev=%d\n", p, c, _LLU(*offset), pg_len, si.dev, si.par_dev); BUG_ON(!page); return _add_to_r4w(ios, &si, page, pg_len); }

Contributors

PersonTokensPropCommitsCommitProp
Boaz Harrosh135100.00%3100.00%
Total135100.00%3100.00%


static void _mark_read4write_pages_uptodate(struct ore_io_state *ios, int ret) { struct bio_vec *bv; unsigned i, d; /* loop on all devices all pages */ for (d = 0; d < ios->numdevs; d++) { struct bio *bio = ios->per_dev[d].bio; if (!bio) continue; bio_for_each_segment_all(bv, bio, i) { struct page *page = bv->bv_page; SetPageUptodate(page); if (PageError(page)) ClearPageError(page); } } }

Contributors

PersonTokensPropCommitsCommitProp
Boaz Harrosh9798.98%150.00%
Kent Overstreet11.02%150.00%
Total98100.00%2100.00%

/* read_4_write is hacked to read the start of the first stripe and/or * the end of the last stripe. If needed, with an sg-gap at each device/page. * It is assumed to be called after the to_be_written pages of the first stripe * are populating ios->sp2d[][] * * NOTE: We call ios->r4w->lock_fn for all pages needed for parity calculations * These pages are held at sp2d[p].pages[c] but with * sp2d[p].page_is_read[c] = true. At _sp2d_reset these pages are * ios->r4w->lock_fn(). The ios->r4w->lock_fn might signal that the page is * @uptodate=true, so we don't need to read it, only unlock, after IO. * * TODO: The read_4_write should calc a need_to_read_pages_count, if bigger then * to-be-written count, we should consider the xor-in-place mode. * need_to_read_pages_count is the actual number of pages not present in cache. * maybe "devs_in_group - ios->sp2d[p].write_count" is a good enough * approximation? In this mode the read pages are put in the empty places of * ios->sp2d[p][*], xor is calculated the same way. These pages are * allocated/freed and don't go through cache */
static int _read_4_write_first_stripe(struct ore_io_state *ios) { struct ore_striping_info read_si; struct __stripe_pages_2d *sp2d = ios->sp2d; u64 offset = ios->si.first_stripe_start; unsigned c, p, min_p = sp2d->pages_in_unit, max_p = -1; if (offset == ios->offset) /* Go to start collect $200 */ goto read_last_stripe; min_p = _sp2d_min_pg(sp2d); max_p = _sp2d_max_pg(sp2d); ORE_DBGMSG("stripe_start=0x%llx ios->offset=0x%llx min_p=%d max_p=%d\n", offset, ios->offset, min_p, max_p); for (c = 0; ; c++) { ore_calc_stripe_info(ios->layout, offset, 0, &read_si); read_si.obj_offset += min_p * PAGE_SIZE; offset += min_p * PAGE_SIZE; for (p = min_p; p <= max_p; p++) { struct __1_page_stripe *_1ps = &sp2d->_1p_stripes[p]; struct page **pp = &_1ps->pages[c]; bool uptodate; if (*pp) { if (ios->offset % PAGE_SIZE) /* Read the remainder of the page */ _add_to_r4w_first_page(ios, *pp); /* to-be-written pages start here */ goto read_last_stripe; } *pp = ios->r4w->get_page(ios->private, offset, &uptodate); if (unlikely(!*pp)) return -ENOMEM; if (!uptodate) _add_to_r4w(ios, &read_si, *pp, PAGE_SIZE); /* Mark read-pages to be cache_released */ _1ps->page_is_read[c] = true; read_si.obj_offset += PAGE_SIZE; offset += PAGE_SIZE; } offset += (sp2d->pages_in_unit - p) * PAGE_SIZE; } read_last_stripe: return 0; }

Contributors

PersonTokensPropCommitsCommitProp
Boaz Harrosh290100.00%3100.00%
Total290100.00%3100.00%


static int _read_4_write_last_stripe(struct ore_io_state *ios) { struct ore_striping_info read_si; struct __stripe_pages_2d *sp2d = ios->sp2d; u64 offset; u64 last_stripe_end; unsigned bytes_in_stripe = ios->si.bytes_in_stripe; unsigned c, p, min_p = sp2d->pages_in_unit, max_p = -1; offset = ios->offset + ios->length; if (offset % PAGE_SIZE) _add_to_r4w_last_page(ios, &offset); /* offset will be aligned to next page */ last_stripe_end = div_u64(offset + bytes_in_stripe - 1, bytes_in_stripe) * bytes_in_stripe; if (offset == last_stripe_end) /* Optimize for the aligned case */ goto read_it; ore_calc_stripe_info(ios->layout, offset, 0, &read_si); p = read_si.cur_pg; c = read_si.cur_comp; if (min_p == sp2d->pages_in_unit) { /* Didn't do it yet */ min_p = _sp2d_min_pg(sp2d); max_p = _sp2d_max_pg(sp2d); } ORE_DBGMSG("offset=0x%llx stripe_end=0x%llx min_p=%d max_p=%d\n", offset, last_stripe_end, min_p, max_p); while (offset < last_stripe_end) { struct __1_page_stripe *_1ps = &sp2d->_1p_stripes[p]; if ((min_p <= p) && (p <= max_p)) { struct page *page; bool uptodate; BUG_ON(_1ps->pages[c]); page = ios->r4w->get_page(ios->private, offset, &uptodate); if (unlikely(!page)) return -ENOMEM; _1ps->pages[c] = page; /* Mark read-pages to be cache_released */ _1ps->page_is_read[c] = true; if (!uptodate) _add_to_r4w(ios, &read_si, page, PAGE_SIZE); } offset += PAGE_SIZE; if (p == (sp2d->pages_in_unit - 1)) { ++c; p = 0; ore_calc_stripe_info(ios->layout, offset, 0, &read_si); } else { read_si.obj_offset += PAGE_SIZE; ++p; } } read_it: return 0; }

Contributors

PersonTokensPropCommitsCommitProp
Boaz Harrosh346100.00%5100.00%
Total346100.00%5100.00%


static int _read_4_write_execute(struct ore_io_state *ios) { struct ore_io_state *ios_read; unsigned i; int ret; ios_read = ios->ios_read_4_write; if (!ios_read) return 0; /* FIXME: Ugly to signal _sbi_read_mirror that we have bio(s). Change * to check for per_dev->bio */ ios_read->pages = ios->pages; /* Now read these devices */ for (i = 0; i < ios_read->numdevs; i += ios_read->layout->mirrors_p1) { ret = _ore_read_mirror(ios_read, i); if (unlikely(ret)) return ret; } ret = ore_io_execute(ios_read); /* Synchronus execution */ if (unlikely(ret)) { ORE_DBGMSG("!! ore_io_execute => %d\n", ret); return ret; } _mark_read4write_pages_uptodate(ios_read, ret); ore_put_io_state(ios_read); ios->ios_read_4_write = NULL; /* Might need a reuse at last stripe */ return 0; }

Contributors

PersonTokensPropCommitsCommitProp
Boaz Harrosh136100.00%3100.00%
Total136100.00%3100.00%

/* In writes @cur_len means length left. .i.e cur_len==0 is the last parity U */
int _ore_add_parity_unit(struct ore_io_state *ios, struct ore_striping_info *si, struct ore_per_dev_state *per_dev, unsigned cur_len, bool do_xor) { if (ios->reading) { if (per_dev->cur_sg >= ios->sgs_per_dev) { ORE_DBGMSG("cur_sg(%d) >= sgs_per_dev(%d)\n" , per_dev->cur_sg, ios->sgs_per_dev); return -ENOMEM; } _ore_add_sg_seg(per_dev, cur_len, true); } else { struct __stripe_pages_2d *sp2d = ios->sp2d; struct page **pages = ios->parity_pages + ios->cur_par_page; unsigned num_pages; unsigned array_start = 0; unsigned i; int ret; si->cur_pg = _sp2d_min_pg(sp2d); num_pages = _sp2d_max_pg(sp2d) + 1 - si->cur_pg; if (!per_dev->length) { per_dev->offset += si->cur_pg * PAGE_SIZE; /* If first stripe, Read in all read4write pages * (if needed) before we calculate the first parity. */ if (do_xor) _read_4_write_first_stripe(ios); } if (!cur_len && do_xor) /* If last stripe r4w pages of last stripe */ _read_4_write_last_stripe(ios); _read_4_write_execute(ios); for (i = 0; i < num_pages; i++) { pages[i] = _raid_page_alloc(); if (unlikely(!pages[i])) return -ENOMEM; ++(ios->cur_par_page); } BUG_ON(si->cur_comp < sp2d->data_devs); BUG_ON(si->cur_pg + num_pages > sp2d->pages_in_unit); ret = _ore_add_stripe_unit(ios, &array_start, 0, pages, per_dev, num_pages * PAGE_SIZE); if (unlikely(ret)) return ret; if (do_xor) { _gen_xor_unit(sp2d); _sp2d_reset(sp2d, ios->r4w, ios->private); } } return 0; }

Contributors

PersonTokensPropCommitsCommitProp
Boaz Harrosh307100.00%5100.00%
Total307100.00%5100.00%


int _ore_post_alloc_raid_stuff(struct ore_io_state *ios) { if (ios->parity_pages) { struct ore_layout *layout = ios->layout; unsigned pages_in_unit = layout->stripe_unit / PAGE_SIZE; if (_sp2d_alloc(pages_in_unit, layout->group_width, layout->parity, &ios->sp2d)) { return -ENOMEM; } } return 0; }

Contributors

PersonTokensPropCommitsCommitProp
Boaz Harrosh65100.00%3100.00%
Total65100.00%3100.00%


void _ore_free_raid_stuff(struct ore_io_state *ios) { if (ios->sp2d) { /* writing and raid */ unsigned i; for (i = 0; i < ios->cur_par_page; i++) { struct page *page = ios->parity_pages[i];