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ftl: more comments

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This commit is contained in:
S.J.R. van Schaik 2017-05-15 16:45:40 +02:00
parent 51893666a5
commit da30898794
1 changed files with 24 additions and 0 deletions
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24
source/ftl/ftl.c
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@ -439,6 +439,12 @@ err_not_found:
static int ftl_write_upage(struct ftl_journal *j, const uint8_t *page,
const struct ftl_page_desc *page_desc);
/* For a given user page, attempt to claim more free space by checking if no
* recent mapping has obsoleted the older mapping. If a more recent mapping
* exists, the page can be safely ignored and erased. Otherwise, we preserve
* the page by copying the page to create a new mapping such that the old page
* can be ignored and erased.
*/
static int free_page(struct ftl_journal *j, uint32_t upage)
{
struct ftl_page_desc page_desc;
@ -462,6 +468,10 @@ static int free_page(struct ftl_journal *j, uint32_t upage)
return ftl_write_upage(j, NULL, &page_desc);
}
/* Claim more free space by checking which user pages in a page group are
* mapped and for which the mappings have been obsoleted by a more recent
* mapping. The mapped user pages are preserved by copying.
*/
static int free_group(struct ftl_journal *j, uint32_t group)
{
uint32_t npages = UINT32_C(1) << j->log2_pages_per_group;
@ -476,6 +486,10 @@ static int free_group(struct ftl_journal *j, uint32_t group)
return 0;
}
/* Claim more free space by checking which user pages in a block are mapped and
* for which the mappings have been obsoleted by a more recent mapping. The
* mapped user pages are preserved by copying.
*/
static int free_block(struct ftl_journal *j, uint32_t block)
{
uint32_t ngroups = UINT32_C(1) << j->log2_groups_per_block;
@ -490,6 +504,11 @@ static int free_block(struct ftl_journal *j, uint32_t block)
return 0;
}
/* Checks if there are sufficient pages available for writing. Otherwise this
* function attempts to claim more free space from unmapped pages for which
* newer pages have obsoleted the mapping. Further, we move the user pages that
* are still mapped as these should be preserved.
*/
static int free_tail(struct ftl_journal *j)
{
size_t log2_pages_per_block = j->log2_pages_per_group +
@ -516,6 +535,11 @@ static int free_tail(struct ftl_journal *j)
return 0;
}
/* Prepare the head for writing. If the user page to be written to is not
* aligned on a block boundary, the block must already be erased and there is
* nothing to be done. Otherwise, we free the tail if necessary and erase the
* block for writing.
*/
static int prepare_head(struct ftl_journal *j)
{
size_t log2_pages_per_block = j->log2_pages_per_group +